changeset 874:4dd230fa84f8

fix crash when calculating large diff, added MoinMoin.support.difflib (ported from 1.5)
author Thomas Waldmann <tw AT waldmann-edv DOT de>
date Sun, 25 Jun 2006 14:41:11 +0200
parents 5019723cb7d4
children 79947ec4347b
files MoinMoin/action/LikePages.py MoinMoin/support/difflib.py MoinMoin/util/diff.py MoinMoin/wikiutil.py docs/CHANGES
diffstat 5 files changed, 2034 insertions(+), 6 deletions(-) [+]
line wrap: on
line diff
--- a/MoinMoin/action/LikePages.py	Sat Jun 24 20:43:47 2006 +0200
+++ b/MoinMoin/action/LikePages.py	Sun Jun 25 14:41:11 2006 +0200
@@ -12,6 +12,8 @@
 """
 
 import re
+
+from MoinMoin.support import difflib
 from MoinMoin import config, wikiutil
 from MoinMoin.Page import Page
 
@@ -81,7 +83,7 @@
     start, end, matches = wikiMatches(pagename, pages, start_re=s_re,
                                       end_re=e_re)
 
-    # Get the best 10 close matches using difflib
+    # Get the best 10 close matches
     close_matches = {}
     found = 0
     for name in closeMatches(pagename, pages):
@@ -167,7 +169,7 @@
 
 
 def closeMatches(pagename, pages):
-    """ Get close matches using difflib
+    """ Get close matches.
 
     Return all matching pages with rank above cutoff value.
 
@@ -176,8 +178,6 @@
     @rtype: list
     @return: list of matching pages, sorted by rank
     """
-    import difflib
-    
     # Match using case insensitive matching
     # Make mapping from lowerpages to pages - pages might have same name
     # with different case (although its stupid).
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MoinMoin/support/difflib.py	Sun Jun 25 14:41:11 2006 +0200
@@ -0,0 +1,2026 @@
+#! /usr/bin/env python
+# Python 2.4.3 (maybe other versions, too) has a broken difflib, sometimes
+# raising a "maximum recursion depth exceeded in cmp" exception.
+# This is taken from python.org SVN repo revision 46940 with patches
+# 36160 and 34415 reversed for python2.3 compatibility.
+
+"""
+Module difflib -- helpers for computing deltas between objects.
+
+Function get_close_matches(word, possibilities, n=3, cutoff=0.6):
+    Use SequenceMatcher to return list of the best "good enough" matches.
+
+Function context_diff(a, b):
+    For two lists of strings, return a delta in context diff format.
+
+Function ndiff(a, b):
+    Return a delta: the difference between `a` and `b` (lists of strings).
+
+Function restore(delta, which):
+    Return one of the two sequences that generated an ndiff delta.
+
+Function unified_diff(a, b):
+    For two lists of strings, return a delta in unified diff format.
+
+Class SequenceMatcher:
+    A flexible class for comparing pairs of sequences of any type.
+
+Class Differ:
+    For producing human-readable deltas from sequences of lines of text.
+
+Class HtmlDiff:
+    For producing HTML side by side comparison with change highlights.
+"""
+
+__all__ = ['get_close_matches', 'ndiff', 'restore', 'SequenceMatcher',
+           'Differ','IS_CHARACTER_JUNK', 'IS_LINE_JUNK', 'context_diff',
+           'unified_diff', 'HtmlDiff']
+
+def _calculate_ratio(matches, length):
+    if length:
+        return 2.0 * matches / length
+    return 1.0
+
+class SequenceMatcher:
+
+    """
+    SequenceMatcher is a flexible class for comparing pairs of sequences of
+    any type, so long as the sequence elements are hashable.  The basic
+    algorithm predates, and is a little fancier than, an algorithm
+    published in the late 1980's by Ratcliff and Obershelp under the
+    hyperbolic name "gestalt pattern matching".  The basic idea is to find
+    the longest contiguous matching subsequence that contains no "junk"
+    elements (R-O doesn't address junk).  The same idea is then applied
+    recursively to the pieces of the sequences to the left and to the right
+    of the matching subsequence.  This does not yield minimal edit
+    sequences, but does tend to yield matches that "look right" to people.
+
+    SequenceMatcher tries to compute a "human-friendly diff" between two
+    sequences.  Unlike e.g. UNIX(tm) diff, the fundamental notion is the
+    longest *contiguous* & junk-free matching subsequence.  That's what
+    catches peoples' eyes.  The Windows(tm) windiff has another interesting
+    notion, pairing up elements that appear uniquely in each sequence.
+    That, and the method here, appear to yield more intuitive difference
+    reports than does diff.  This method appears to be the least vulnerable
+    to synching up on blocks of "junk lines", though (like blank lines in
+    ordinary text files, or maybe "<P>" lines in HTML files).  That may be
+    because this is the only method of the 3 that has a *concept* of
+    "junk" <wink>.
+
+    Example, comparing two strings, and considering blanks to be "junk":
+
+    >>> s = SequenceMatcher(lambda x: x == " ",
+    ...                     "private Thread currentThread;",
+    ...                     "private volatile Thread currentThread;")
+    >>>
+
+    .ratio() returns a float in [0, 1], measuring the "similarity" of the
+    sequences.  As a rule of thumb, a .ratio() value over 0.6 means the
+    sequences are close matches:
+
+    >>> print round(s.ratio(), 3)
+    0.866
+    >>>
+
+    If you're only interested in where the sequences match,
+    .get_matching_blocks() is handy:
+
+    >>> for block in s.get_matching_blocks():
+    ...     print "a[%d] and b[%d] match for %d elements" % block
+    a[0] and b[0] match for 8 elements
+    a[8] and b[17] match for 21 elements
+    a[29] and b[38] match for 0 elements
+
+    Note that the last tuple returned by .get_matching_blocks() is always a
+    dummy, (len(a), len(b), 0), and this is the only case in which the last
+    tuple element (number of elements matched) is 0.
+
+    If you want to know how to change the first sequence into the second,
+    use .get_opcodes():
+
+    >>> for opcode in s.get_opcodes():
+    ...     print "%6s a[%d:%d] b[%d:%d]" % opcode
+     equal a[0:8] b[0:8]
+    insert a[8:8] b[8:17]
+     equal a[8:29] b[17:38]
+
+    See the Differ class for a fancy human-friendly file differencer, which
+    uses SequenceMatcher both to compare sequences of lines, and to compare
+    sequences of characters within similar (near-matching) lines.
+
+    See also function get_close_matches() in this module, which shows how
+    simple code building on SequenceMatcher can be used to do useful work.
+
+    Timing:  Basic R-O is cubic time worst case and quadratic time expected
+    case.  SequenceMatcher is quadratic time for the worst case and has
+    expected-case behavior dependent in a complicated way on how many
+    elements the sequences have in common; best case time is linear.
+
+    Methods:
+
+    __init__(isjunk=None, a='', b='')
+        Construct a SequenceMatcher.
+
+    set_seqs(a, b)
+        Set the two sequences to be compared.
+
+    set_seq1(a)
+        Set the first sequence to be compared.
+
+    set_seq2(b)
+        Set the second sequence to be compared.
+
+    find_longest_match(alo, ahi, blo, bhi)
+        Find longest matching block in a[alo:ahi] and b[blo:bhi].
+
+    get_matching_blocks()
+        Return list of triples describing matching subsequences.
+
+    get_opcodes()
+        Return list of 5-tuples describing how to turn a into b.
+
+    ratio()
+        Return a measure of the sequences' similarity (float in [0,1]).
+
+    quick_ratio()
+        Return an upper bound on .ratio() relatively quickly.
+
+    real_quick_ratio()
+        Return an upper bound on ratio() very quickly.
+    """
+
+    def __init__(self, isjunk=None, a='', b=''):
+        """Construct a SequenceMatcher.
+
+        Optional arg isjunk is None (the default), or a one-argument
+        function that takes a sequence element and returns true iff the
+        element is junk.  None is equivalent to passing "lambda x: 0", i.e.
+        no elements are considered to be junk.  For example, pass
+            lambda x: x in " \\t"
+        if you're comparing lines as sequences of characters, and don't
+        want to synch up on blanks or hard tabs.
+
+        Optional arg a is the first of two sequences to be compared.  By
+        default, an empty string.  The elements of a must be hashable.  See
+        also .set_seqs() and .set_seq1().
+
+        Optional arg b is the second of two sequences to be compared.  By
+        default, an empty string.  The elements of b must be hashable. See
+        also .set_seqs() and .set_seq2().
+        """
+
+        # Members:
+        # a
+        #      first sequence
+        # b
+        #      second sequence; differences are computed as "what do
+        #      we need to do to 'a' to change it into 'b'?"
+        # b2j
+        #      for x in b, b2j[x] is a list of the indices (into b)
+        #      at which x appears; junk elements do not appear
+        # fullbcount
+        #      for x in b, fullbcount[x] == the number of times x
+        #      appears in b; only materialized if really needed (used
+        #      only for computing quick_ratio())
+        # matching_blocks
+        #      a list of (i, j, k) triples, where a[i:i+k] == b[j:j+k];
+        #      ascending & non-overlapping in i and in j; terminated by
+        #      a dummy (len(a), len(b), 0) sentinel
+        # opcodes
+        #      a list of (tag, i1, i2, j1, j2) tuples, where tag is
+        #      one of
+        #          'replace'   a[i1:i2] should be replaced by b[j1:j2]
+        #          'delete'    a[i1:i2] should be deleted
+        #          'insert'    b[j1:j2] should be inserted
+        #          'equal'     a[i1:i2] == b[j1:j2]
+        # isjunk
+        #      a user-supplied function taking a sequence element and
+        #      returning true iff the element is "junk" -- this has
+        #      subtle but helpful effects on the algorithm, which I'll
+        #      get around to writing up someday <0.9 wink>.
+        #      DON'T USE!  Only __chain_b uses this.  Use isbjunk.
+        # isbjunk
+        #      for x in b, isbjunk(x) == isjunk(x) but much faster;
+        #      it's really the has_key method of a hidden dict.
+        #      DOES NOT WORK for x in a!
+        # isbpopular
+        #      for x in b, isbpopular(x) is true iff b is reasonably long
+        #      (at least 200 elements) and x accounts for more than 1% of
+        #      its elements.  DOES NOT WORK for x in a!
+
+        self.isjunk = isjunk
+        self.a = self.b = None
+        self.set_seqs(a, b)
+
+    def set_seqs(self, a, b):
+        """Set the two sequences to be compared.
+
+        >>> s = SequenceMatcher()
+        >>> s.set_seqs("abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        """
+
+        self.set_seq1(a)
+        self.set_seq2(b)
+
+    def set_seq1(self, a):
+        """Set the first sequence to be compared.
+
+        The second sequence to be compared is not changed.
+
+        >>> s = SequenceMatcher(None, "abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        >>> s.set_seq1("bcde")
+        >>> s.ratio()
+        1.0
+        >>>
+
+        SequenceMatcher computes and caches detailed information about the
+        second sequence, so if you want to compare one sequence S against
+        many sequences, use .set_seq2(S) once and call .set_seq1(x)
+        repeatedly for each of the other sequences.
+
+        See also set_seqs() and set_seq2().
+        """
+
+        if a is self.a:
+            return
+        self.a = a
+        self.matching_blocks = self.opcodes = None
+
+    def set_seq2(self, b):
+        """Set the second sequence to be compared.
+
+        The first sequence to be compared is not changed.
+
+        >>> s = SequenceMatcher(None, "abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        >>> s.set_seq2("abcd")
+        >>> s.ratio()
+        1.0
+        >>>
+
+        SequenceMatcher computes and caches detailed information about the
+        second sequence, so if you want to compare one sequence S against
+        many sequences, use .set_seq2(S) once and call .set_seq1(x)
+        repeatedly for each of the other sequences.
+
+        See also set_seqs() and set_seq1().
+        """
+
+        if b is self.b:
+            return
+        self.b = b
+        self.matching_blocks = self.opcodes = None
+        self.fullbcount = None
+        self.__chain_b()
+
+    # For each element x in b, set b2j[x] to a list of the indices in
+    # b where x appears; the indices are in increasing order; note that
+    # the number of times x appears in b is len(b2j[x]) ...
+    # when self.isjunk is defined, junk elements don't show up in this
+    # map at all, which stops the central find_longest_match method
+    # from starting any matching block at a junk element ...
+    # also creates the fast isbjunk function ...
+    # b2j also does not contain entries for "popular" elements, meaning
+    # elements that account for more than 1% of the total elements, and
+    # when the sequence is reasonably large (>= 200 elements); this can
+    # be viewed as an adaptive notion of semi-junk, and yields an enormous
+    # speedup when, e.g., comparing program files with hundreds of
+    # instances of "return NULL;" ...
+    # note that this is only called when b changes; so for cross-product
+    # kinds of matches, it's best to call set_seq2 once, then set_seq1
+    # repeatedly
+
+    def __chain_b(self):
+        # Because isjunk is a user-defined (not C) function, and we test
+        # for junk a LOT, it's important to minimize the number of calls.
+        # Before the tricks described here, __chain_b was by far the most
+        # time-consuming routine in the whole module!  If anyone sees
+        # Jim Roskind, thank him again for profile.py -- I never would
+        # have guessed that.
+        # The first trick is to build b2j ignoring the possibility
+        # of junk.  I.e., we don't call isjunk at all yet.  Throwing
+        # out the junk later is much cheaper than building b2j "right"
+        # from the start.
+        b = self.b
+        n = len(b)
+        self.b2j = b2j = {}
+        populardict = {}
+        for i, elt in enumerate(b):
+            if elt in b2j:
+                indices = b2j[elt]
+                if n >= 200 and len(indices) * 100 > n:
+                    populardict[elt] = 1
+                    del indices[:]
+                else:
+                    indices.append(i)
+            else:
+                b2j[elt] = [i]
+
+        # Purge leftover indices for popular elements.
+        for elt in populardict:
+            del b2j[elt]
+
+        # Now b2j.keys() contains elements uniquely, and especially when
+        # the sequence is a string, that's usually a good deal smaller
+        # than len(string).  The difference is the number of isjunk calls
+        # saved.
+        isjunk = self.isjunk
+        junkdict = {}
+        if isjunk:
+            for d in populardict, b2j:
+                for elt in d.keys():
+                    if isjunk(elt):
+                        junkdict[elt] = 1
+                        del d[elt]
+
+        # Now for x in b, isjunk(x) == x in junkdict, but the
+        # latter is much faster.  Note too that while there may be a
+        # lot of junk in the sequence, the number of *unique* junk
+        # elements is probably small.  So the memory burden of keeping
+        # this dict alive is likely trivial compared to the size of b2j.
+        self.isbjunk = junkdict.has_key
+        self.isbpopular = populardict.has_key
+
+    def find_longest_match(self, alo, ahi, blo, bhi):
+        """Find longest matching block in a[alo:ahi] and b[blo:bhi].
+
+        If isjunk is not defined:
+
+        Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where
+            alo <= i <= i+k <= ahi
+            blo <= j <= j+k <= bhi
+        and for all (i',j',k') meeting those conditions,
+            k >= k'
+            i <= i'
+            and if i == i', j <= j'
+
+        In other words, of all maximal matching blocks, return one that
+        starts earliest in a, and of all those maximal matching blocks that
+        start earliest in a, return the one that starts earliest in b.
+
+        >>> s = SequenceMatcher(None, " abcd", "abcd abcd")
+        >>> s.find_longest_match(0, 5, 0, 9)
+        (0, 4, 5)
+
+        If isjunk is defined, first the longest matching block is
+        determined as above, but with the additional restriction that no
+        junk element appears in the block.  Then that block is extended as
+        far as possible by matching (only) junk elements on both sides.  So
+        the resulting block never matches on junk except as identical junk
+        happens to be adjacent to an "interesting" match.
+
+        Here's the same example as before, but considering blanks to be
+        junk.  That prevents " abcd" from matching the " abcd" at the tail
+        end of the second sequence directly.  Instead only the "abcd" can
+        match, and matches the leftmost "abcd" in the second sequence:
+
+        >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")
+        >>> s.find_longest_match(0, 5, 0, 9)
+        (1, 0, 4)
+
+        If no blocks match, return (alo, blo, 0).
+
+        >>> s = SequenceMatcher(None, "ab", "c")
+        >>> s.find_longest_match(0, 2, 0, 1)
+        (0, 0, 0)
+        """
+
+        # CAUTION:  stripping common prefix or suffix would be incorrect.
+        # E.g.,
+        #    ab
+        #    acab
+        # Longest matching block is "ab", but if common prefix is
+        # stripped, it's "a" (tied with "b").  UNIX(tm) diff does so
+        # strip, so ends up claiming that ab is changed to acab by
+        # inserting "ca" in the middle.  That's minimal but unintuitive:
+        # "it's obvious" that someone inserted "ac" at the front.
+        # Windiff ends up at the same place as diff, but by pairing up
+        # the unique 'b's and then matching the first two 'a's.
+
+        a, b, b2j, isbjunk = self.a, self.b, self.b2j, self.isbjunk
+        besti, bestj, bestsize = alo, blo, 0
+        # find longest junk-free match
+        # during an iteration of the loop, j2len[j] = length of longest
+        # junk-free match ending with a[i-1] and b[j]
+        j2len = {}
+        nothing = []
+        for i in xrange(alo, ahi):
+            # look at all instances of a[i] in b; note that because
+            # b2j has no junk keys, the loop is skipped if a[i] is junk
+            j2lenget = j2len.get
+            newj2len = {}
+            for j in b2j.get(a[i], nothing):
+                # a[i] matches b[j]
+                if j < blo:
+                    continue
+                if j >= bhi:
+                    break
+                k = newj2len[j] = j2lenget(j-1, 0) + 1
+                if k > bestsize:
+                    besti, bestj, bestsize = i-k+1, j-k+1, k
+            j2len = newj2len
+
+        # Extend the best by non-junk elements on each end.  In particular,
+        # "popular" non-junk elements aren't in b2j, which greatly speeds
+        # the inner loop above, but also means "the best" match so far
+        # doesn't contain any junk *or* popular non-junk elements.
+        while besti > alo and bestj > blo and \
+              not isbjunk(b[bestj-1]) and \
+              a[besti-1] == b[bestj-1]:
+            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
+        while besti+bestsize < ahi and bestj+bestsize < bhi and \
+              not isbjunk(b[bestj+bestsize]) and \
+              a[besti+bestsize] == b[bestj+bestsize]:
+            bestsize += 1
+
+        # Now that we have a wholly interesting match (albeit possibly
+        # empty!), we may as well suck up the matching junk on each
+        # side of it too.  Can't think of a good reason not to, and it
+        # saves post-processing the (possibly considerable) expense of
+        # figuring out what to do with it.  In the case of an empty
+        # interesting match, this is clearly the right thing to do,
+        # because no other kind of match is possible in the regions.
+        while besti > alo and bestj > blo and \
+              isbjunk(b[bestj-1]) and \
+              a[besti-1] == b[bestj-1]:
+            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
+        while besti+bestsize < ahi and bestj+bestsize < bhi and \
+              isbjunk(b[bestj+bestsize]) and \
+              a[besti+bestsize] == b[bestj+bestsize]:
+            bestsize = bestsize + 1
+
+        return besti, bestj, bestsize
+
+    def get_matching_blocks(self):
+        """Return list of triples describing matching subsequences.
+
+        Each triple is of the form (i, j, n), and means that
+        a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in
+        i and in j.  New in Python 2.5, it's also guaranteed that if
+        (i, j, n) and (i', j', n') are adjacent triples in the list, and
+        the second is not the last triple in the list, then i+n != i' or
+        j+n != j'.  IOW, adjacent triples never describe adjacent equal
+        blocks.
+
+        The last triple is a dummy, (len(a), len(b), 0), and is the only
+        triple with n==0.
+
+        >>> s = SequenceMatcher(None, "abxcd", "abcd")
+        >>> s.get_matching_blocks()
+        [(0, 0, 2), (3, 2, 2), (5, 4, 0)]
+        """
+
+        if self.matching_blocks is not None:
+            return self.matching_blocks
+        la, lb = len(self.a), len(self.b)
+
+        # This is most naturally expressed as a recursive algorithm, but
+        # at least one user bumped into extreme use cases that exceeded
+        # the recursion limit on their box.  So, now we maintain a list
+        # ('queue`) of blocks we still need to look at, and append partial
+        # results to `matching_blocks` in a loop; the matches are sorted
+        # at the end.
+        queue = [(0, la, 0, lb)]
+        matching_blocks = []
+        while queue:
+            alo, ahi, blo, bhi = queue.pop()
+            i, j, k = x = self.find_longest_match(alo, ahi, blo, bhi)
+            # a[alo:i] vs b[blo:j] unknown
+            # a[i:i+k] same as b[j:j+k]
+            # a[i+k:ahi] vs b[j+k:bhi] unknown
+            if k:   # if k is 0, there was no matching block
+                matching_blocks.append(x)
+                if alo < i and blo < j:
+                    queue.append((alo, i, blo, j))
+                if i+k < ahi and j+k < bhi:
+                    queue.append((i+k, ahi, j+k, bhi))
+        matching_blocks.sort()
+
+        # It's possible that we have adjacent equal blocks in the
+        # matching_blocks list now.  Starting with 2.5, this code was added
+        # to collapse them.
+        i1 = j1 = k1 = 0
+        non_adjacent = []
+        for i2, j2, k2 in matching_blocks:
+            # Is this block adjacent to i1, j1, k1?
+            if i1 + k1 == i2 and j1 + k1 == j2:
+                # Yes, so collapse them -- this just increases the length of
+                # the first block by the length of the second, and the first
+                # block so lengthened remains the block to compare against.
+                k1 += k2
+            else:
+                # Not adjacent.  Remember the first block (k1==0 means it's
+                # the dummy we started with), and make the second block the
+                # new block to compare against.
+                if k1:
+                    non_adjacent.append((i1, j1, k1))
+                i1, j1, k1 = i2, j2, k2
+        if k1:
+            non_adjacent.append((i1, j1, k1))
+
+        non_adjacent.append( (la, lb, 0) )
+        self.matching_blocks = non_adjacent
+        return self.matching_blocks
+
+    def get_opcodes(self):
+        """Return list of 5-tuples describing how to turn a into b.
+
+        Each tuple is of the form (tag, i1, i2, j1, j2).  The first tuple
+        has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the
+        tuple preceding it, and likewise for j1 == the previous j2.
+
+        The tags are strings, with these meanings:
+
+        'replace':  a[i1:i2] should be replaced by b[j1:j2]
+        'delete':   a[i1:i2] should be deleted.
+                    Note that j1==j2 in this case.
+        'insert':   b[j1:j2] should be inserted at a[i1:i1].
+                    Note that i1==i2 in this case.
+        'equal':    a[i1:i2] == b[j1:j2]
+
+        >>> a = "qabxcd"
+        >>> b = "abycdf"
+        >>> s = SequenceMatcher(None, a, b)
+        >>> for tag, i1, i2, j1, j2 in s.get_opcodes():
+        ...    print ("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
+        ...           (tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2]))
+         delete a[0:1] (q) b[0:0] ()
+          equal a[1:3] (ab) b[0:2] (ab)
+        replace a[3:4] (x) b[2:3] (y)
+          equal a[4:6] (cd) b[3:5] (cd)
+         insert a[6:6] () b[5:6] (f)
+        """
+
+        if self.opcodes is not None:
+            return self.opcodes
+        i = j = 0
+        self.opcodes = answer = []
+        for ai, bj, size in self.get_matching_blocks():
+            # invariant:  we've pumped out correct diffs to change
+            # a[:i] into b[:j], and the next matching block is
+            # a[ai:ai+size] == b[bj:bj+size].  So we need to pump
+            # out a diff to change a[i:ai] into b[j:bj], pump out
+            # the matching block, and move (i,j) beyond the match
+            tag = ''
+            if i < ai and j < bj:
+                tag = 'replace'
+            elif i < ai:
+                tag = 'delete'
+            elif j < bj:
+                tag = 'insert'
+            if tag:
+                answer.append( (tag, i, ai, j, bj) )
+            i, j = ai+size, bj+size
+            # the list of matching blocks is terminated by a
+            # sentinel with size 0
+            if size:
+                answer.append( ('equal', ai, i, bj, j) )
+        return answer
+
+    def get_grouped_opcodes(self, n=3):
+        """ Isolate change clusters by eliminating ranges with no changes.
+
+        Return a generator of groups with upto n lines of context.
+        Each group is in the same format as returned by get_opcodes().
+
+        >>> from pprint import pprint
+        >>> a = map(str, range(1,40))
+        >>> b = a[:]
+        >>> b[8:8] = ['i']     # Make an insertion
+        >>> b[20] += 'x'       # Make a replacement
+        >>> b[23:28] = []      # Make a deletion
+        >>> b[30] += 'y'       # Make another replacement
+        >>> pprint(list(SequenceMatcher(None,a,b).get_grouped_opcodes()))
+        [[('equal', 5, 8, 5, 8), ('insert', 8, 8, 8, 9), ('equal', 8, 11, 9, 12)],
+         [('equal', 16, 19, 17, 20),
+          ('replace', 19, 20, 20, 21),
+          ('equal', 20, 22, 21, 23),
+          ('delete', 22, 27, 23, 23),
+          ('equal', 27, 30, 23, 26)],
+         [('equal', 31, 34, 27, 30),
+          ('replace', 34, 35, 30, 31),
+          ('equal', 35, 38, 31, 34)]]
+        """
+
+        codes = self.get_opcodes()
+        if not codes:
+            codes = [("equal", 0, 1, 0, 1)]
+        # Fixup leading and trailing groups if they show no changes.
+        if codes[0][0] == 'equal':
+            tag, i1, i2, j1, j2 = codes[0]
+            codes[0] = tag, max(i1, i2-n), i2, max(j1, j2-n), j2
+        if codes[-1][0] == 'equal':
+            tag, i1, i2, j1, j2 = codes[-1]
+            codes[-1] = tag, i1, min(i2, i1+n), j1, min(j2, j1+n)
+
+        nn = n + n
+        group = []
+        for tag, i1, i2, j1, j2 in codes:
+            # End the current group and start a new one whenever
+            # there is a large range with no changes.
+            if tag == 'equal' and i2-i1 > nn:
+                group.append((tag, i1, min(i2, i1+n), j1, min(j2, j1+n)))
+                yield group
+                group = []
+                i1, j1 = max(i1, i2-n), max(j1, j2-n)
+            group.append((tag, i1, i2, j1 ,j2))
+        if group and not (len(group)==1 and group[0][0] == 'equal'):
+            yield group
+
+    def ratio(self):
+        """Return a measure of the sequences' similarity (float in [0,1]).
+
+        Where T is the total number of elements in both sequences, and
+        M is the number of matches, this is 2.0*M / T.
+        Note that this is 1 if the sequences are identical, and 0 if
+        they have nothing in common.
+
+        .ratio() is expensive to compute if you haven't already computed
+        .get_matching_blocks() or .get_opcodes(), in which case you may
+        want to try .quick_ratio() or .real_quick_ratio() first to get an
+        upper bound.
+
+        >>> s = SequenceMatcher(None, "abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        >>> s.quick_ratio()
+        0.75
+        >>> s.real_quick_ratio()
+        1.0
+        """
+
+        matches = reduce(lambda sum, triple: sum + triple[-1],
+                         self.get_matching_blocks(), 0)
+        return _calculate_ratio(matches, len(self.a) + len(self.b))
+
+    def quick_ratio(self):
+        """Return an upper bound on ratio() relatively quickly.
+
+        This isn't defined beyond that it is an upper bound on .ratio(), and
+        is faster to compute.
+        """
+
+        # viewing a and b as multisets, set matches to the cardinality
+        # of their intersection; this counts the number of matches
+        # without regard to order, so is clearly an upper bound
+        if self.fullbcount is None:
+            self.fullbcount = fullbcount = {}
+            for elt in self.b:
+                fullbcount[elt] = fullbcount.get(elt, 0) + 1
+        fullbcount = self.fullbcount
+        # avail[x] is the number of times x appears in 'b' less the
+        # number of times we've seen it in 'a' so far ... kinda
+        avail = {}
+        availhas, matches = avail.has_key, 0
+        for elt in self.a:
+            if availhas(elt):
+                numb = avail[elt]
+            else:
+                numb = fullbcount.get(elt, 0)
+            avail[elt] = numb - 1
+            if numb > 0:
+                matches = matches + 1
+        return _calculate_ratio(matches, len(self.a) + len(self.b))
+
+    def real_quick_ratio(self):
+        """Return an upper bound on ratio() very quickly.
+
+        This isn't defined beyond that it is an upper bound on .ratio(), and
+        is faster to compute than either .ratio() or .quick_ratio().
+        """
+
+        la, lb = len(self.a), len(self.b)
+        # can't have more matches than the number of elements in the
+        # shorter sequence
+        return _calculate_ratio(min(la, lb), la + lb)
+
+def get_close_matches(word, possibilities, n=3, cutoff=0.6):
+    """Use SequenceMatcher to return list of the best "good enough" matches.
+
+    word is a sequence for which close matches are desired (typically a
+    string).
+
+    possibilities is a list of sequences against which to match word
+    (typically a list of strings).
+
+    Optional arg n (default 3) is the maximum number of close matches to
+    return.  n must be > 0.
+
+    Optional arg cutoff (default 0.6) is a float in [0, 1].  Possibilities
+    that don't score at least that similar to word are ignored.
+
+    The best (no more than n) matches among the possibilities are returned
+    in a list, sorted by similarity score, most similar first.
+
+    >>> get_close_matches("appel", ["ape", "apple", "peach", "puppy"])
+    ['apple', 'ape']
+    >>> import keyword as _keyword
+    >>> get_close_matches("wheel", _keyword.kwlist)
+    ['while']
+    >>> get_close_matches("apple", _keyword.kwlist)
+    []
+    >>> get_close_matches("accept", _keyword.kwlist)
+    ['except']
+    """
+
+    if not n >  0:
+        raise ValueError("n must be > 0: %r" % (n,))
+    if not 0.0 <= cutoff <= 1.0:
+        raise ValueError("cutoff must be in [0.0, 1.0]: %r" % (cutoff,))
+    result = []
+    s = SequenceMatcher()
+    s.set_seq2(word)
+    for x in possibilities:
+        s.set_seq1(x)
+        if s.real_quick_ratio() >= cutoff and \
+           s.quick_ratio() >= cutoff and \
+           s.ratio() >= cutoff:
+            result.append((s.ratio(), x))
+
+    # Sort by score.    
+    result.sort()   
+    # Retain only the best n.   
+    result = result[-n:]    
+    # Move best-scorer to head of list.     
+    result.reverse()    
+    # Strip scores.     
+    return [x for score, x in result]
+
+def _count_leading(line, ch):
+    """
+    Return number of `ch` characters at the start of `line`.
+
+    Example:
+
+    >>> _count_leading('   abc', ' ')
+    3
+    """
+
+    i, n = 0, len(line)
+    while i < n and line[i] == ch:
+        i += 1
+    return i
+
+class Differ:
+    r"""
+    Differ is a class for comparing sequences of lines of text, and
+    producing human-readable differences or deltas.  Differ uses
+    SequenceMatcher both to compare sequences of lines, and to compare
+    sequences of characters within similar (near-matching) lines.
+
+    Each line of a Differ delta begins with a two-letter code:
+
+        '- '    line unique to sequence 1
+        '+ '    line unique to sequence 2
+        '  '    line common to both sequences
+        '? '    line not present in either input sequence
+
+    Lines beginning with '? ' attempt to guide the eye to intraline
+    differences, and were not present in either input sequence.  These lines
+    can be confusing if the sequences contain tab characters.
+
+    Note that Differ makes no claim to produce a *minimal* diff.  To the
+    contrary, minimal diffs are often counter-intuitive, because they synch
+    up anywhere possible, sometimes accidental matches 100 pages apart.
+    Restricting synch points to contiguous matches preserves some notion of
+    locality, at the occasional cost of producing a longer diff.
+
+    Example: Comparing two texts.
+
+    First we set up the texts, sequences of individual single-line strings
+    ending with newlines (such sequences can also be obtained from the
+    `readlines()` method of file-like objects):
+
+    >>> text1 = '''  1. Beautiful is better than ugly.
+    ...   2. Explicit is better than implicit.
+    ...   3. Simple is better than complex.
+    ...   4. Complex is better than complicated.
+    ... '''.splitlines(1)
+    >>> len(text1)
+    4
+    >>> text1[0][-1]
+    '\n'
+    >>> text2 = '''  1. Beautiful is better than ugly.
+    ...   3.   Simple is better than complex.
+    ...   4. Complicated is better than complex.
+    ...   5. Flat is better than nested.
+    ... '''.splitlines(1)
+
+    Next we instantiate a Differ object:
+
+    >>> d = Differ()
+
+    Note that when instantiating a Differ object we may pass functions to
+    filter out line and character 'junk'.  See Differ.__init__ for details.
+
+    Finally, we compare the two:
+
+    >>> result = list(d.compare(text1, text2))
+
+    'result' is a list of strings, so let's pretty-print it:
+
+    >>> from pprint import pprint as _pprint
+    >>> _pprint(result)
+    ['    1. Beautiful is better than ugly.\n',
+     '-   2. Explicit is better than implicit.\n',
+     '-   3. Simple is better than complex.\n',
+     '+   3.   Simple is better than complex.\n',
+     '?     ++\n',
+     '-   4. Complex is better than complicated.\n',
+     '?            ^                     ---- ^\n',
+     '+   4. Complicated is better than complex.\n',
+     '?           ++++ ^                      ^\n',
+     '+   5. Flat is better than nested.\n']
+
+    As a single multi-line string it looks like this:
+
+    >>> print ''.join(result),
+        1. Beautiful is better than ugly.
+    -   2. Explicit is better than implicit.
+    -   3. Simple is better than complex.
+    +   3.   Simple is better than complex.
+    ?     ++
+    -   4. Complex is better than complicated.
+    ?            ^                     ---- ^
+    +   4. Complicated is better than complex.
+    ?           ++++ ^                      ^
+    +   5. Flat is better than nested.
+
+    Methods:
+
+    __init__(linejunk=None, charjunk=None)
+        Construct a text differencer, with optional filters.
+
+    compare(a, b)
+        Compare two sequences of lines; generate the resulting delta.
+    """
+
+    def __init__(self, linejunk=None, charjunk=None):
+        """
+        Construct a text differencer, with optional filters.
+
+        The two optional keyword parameters are for filter functions:
+
+        - `linejunk`: A function that should accept a single string argument,
+          and return true iff the string is junk. The module-level function
+          `IS_LINE_JUNK` may be used to filter out lines without visible
+          characters, except for at most one splat ('#').  It is recommended
+          to leave linejunk None; as of Python 2.3, the underlying
+          SequenceMatcher class has grown an adaptive notion of "noise" lines
+          that's better than any static definition the author has ever been
+          able to craft.
+
+        - `charjunk`: A function that should accept a string of length 1. The
+          module-level function `IS_CHARACTER_JUNK` may be used to filter out
+          whitespace characters (a blank or tab; **note**: bad idea to include
+          newline in this!).  Use of IS_CHARACTER_JUNK is recommended.
+        """
+
+        self.linejunk = linejunk
+        self.charjunk = charjunk
+
+    def compare(self, a, b):
+        r"""
+        Compare two sequences of lines; generate the resulting delta.
+
+        Each sequence must contain individual single-line strings ending with
+        newlines. Such sequences can be obtained from the `readlines()` method
+        of file-like objects.  The delta generated also consists of newline-
+        terminated strings, ready to be printed as-is via the writeline()
+        method of a file-like object.
+
+        Example:
+
+        >>> print ''.join(Differ().compare('one\ntwo\nthree\n'.splitlines(1),
+        ...                                'ore\ntree\nemu\n'.splitlines(1))),
+        - one
+        ?  ^
+        + ore
+        ?  ^
+        - two
+        - three
+        ?  -
+        + tree
+        + emu
+        """
+
+        cruncher = SequenceMatcher(self.linejunk, a, b)
+        for tag, alo, ahi, blo, bhi in cruncher.get_opcodes():
+            if tag == 'replace':
+                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
+            elif tag == 'delete':
+                g = self._dump('-', a, alo, ahi)
+            elif tag == 'insert':
+                g = self._dump('+', b, blo, bhi)
+            elif tag == 'equal':
+                g = self._dump(' ', a, alo, ahi)
+            else:
+                raise ValueError, 'unknown tag %r' % (tag,)
+
+            for line in g:
+                yield line
+
+    def _dump(self, tag, x, lo, hi):
+        """Generate comparison results for a same-tagged range."""
+        for i in xrange(lo, hi):
+            yield '%s %s' % (tag, x[i])
+
+    def _plain_replace(self, a, alo, ahi, b, blo, bhi):
+        assert alo < ahi and blo < bhi
+        # dump the shorter block first -- reduces the burden on short-term
+        # memory if the blocks are of very different sizes
+        if bhi - blo < ahi - alo:
+            first  = self._dump('+', b, blo, bhi)
+            second = self._dump('-', a, alo, ahi)
+        else:
+            first  = self._dump('-', a, alo, ahi)
+            second = self._dump('+', b, blo, bhi)
+
+        for g in first, second:
+            for line in g:
+                yield line
+
+    def _fancy_replace(self, a, alo, ahi, b, blo, bhi):
+        r"""
+        When replacing one block of lines with another, search the blocks
+        for *similar* lines; the best-matching pair (if any) is used as a
+        synch point, and intraline difference marking is done on the
+        similar pair. Lots of work, but often worth it.
+
+        Example:
+
+        >>> d = Differ()
+        >>> results = d._fancy_replace(['abcDefghiJkl\n'], 0, 1,
+        ...                            ['abcdefGhijkl\n'], 0, 1)
+        >>> print ''.join(results),
+        - abcDefghiJkl
+        ?    ^  ^  ^
+        + abcdefGhijkl
+        ?    ^  ^  ^
+        """
+
+        # don't synch up unless the lines have a similarity score of at
+        # least cutoff; best_ratio tracks the best score seen so far
+        best_ratio, cutoff = 0.74, 0.75
+        cruncher = SequenceMatcher(self.charjunk)
+        eqi, eqj = None, None   # 1st indices of equal lines (if any)
+
+        # search for the pair that matches best without being identical
+        # (identical lines must be junk lines, & we don't want to synch up
+        # on junk -- unless we have to)
+        for j in xrange(blo, bhi):
+            bj = b[j]
+            cruncher.set_seq2(bj)
+            for i in xrange(alo, ahi):
+                ai = a[i]
+                if ai == bj:
+                    if eqi is None:
+                        eqi, eqj = i, j
+                    continue
+                cruncher.set_seq1(ai)
+                # computing similarity is expensive, so use the quick
+                # upper bounds first -- have seen this speed up messy
+                # compares by a factor of 3.
+                # note that ratio() is only expensive to compute the first
+                # time it's called on a sequence pair; the expensive part
+                # of the computation is cached by cruncher
+                if cruncher.real_quick_ratio() > best_ratio and \
+                      cruncher.quick_ratio() > best_ratio and \
+                      cruncher.ratio() > best_ratio:
+                    best_ratio, best_i, best_j = cruncher.ratio(), i, j
+        if best_ratio < cutoff:
+            # no non-identical "pretty close" pair
+            if eqi is None:
+                # no identical pair either -- treat it as a straight replace
+                for line in self._plain_replace(a, alo, ahi, b, blo, bhi):
+                    yield line
+                return
+            # no close pair, but an identical pair -- synch up on that
+            best_i, best_j, best_ratio = eqi, eqj, 1.0
+        else:
+            # there's a close pair, so forget the identical pair (if any)
+            eqi = None
+
+        # a[best_i] very similar to b[best_j]; eqi is None iff they're not
+        # identical
+
+        # pump out diffs from before the synch point
+        for line in self._fancy_helper(a, alo, best_i, b, blo, best_j):
+            yield line
+
+        # do intraline marking on the synch pair
+        aelt, belt = a[best_i], b[best_j]
+        if eqi is None:
+            # pump out a '-', '?', '+', '?' quad for the synched lines
+            atags = btags = ""
+            cruncher.set_seqs(aelt, belt)
+            for tag, ai1, ai2, bj1, bj2 in cruncher.get_opcodes():
+                la, lb = ai2 - ai1, bj2 - bj1
+                if tag == 'replace':
+                    atags += '^' * la
+                    btags += '^' * lb
+                elif tag == 'delete':
+                    atags += '-' * la
+                elif tag == 'insert':
+                    btags += '+' * lb
+                elif tag == 'equal':
+                    atags += ' ' * la
+                    btags += ' ' * lb
+                else:
+                    raise ValueError, 'unknown tag %r' % (tag,)
+            for line in self._qformat(aelt, belt, atags, btags):
+                yield line
+        else:
+            # the synch pair is identical
+            yield '  ' + aelt
+
+        # pump out diffs from after the synch point
+        for line in self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi):
+            yield line
+
+    def _fancy_helper(self, a, alo, ahi, b, blo, bhi):
+        g = []
+        if alo < ahi:
+            if blo < bhi:
+                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
+            else:
+                g = self._dump('-', a, alo, ahi)
+        elif blo < bhi:
+            g = self._dump('+', b, blo, bhi)
+
+        for line in g:
+            yield line
+
+    def _qformat(self, aline, bline, atags, btags):
+        r"""
+        Format "?" output and deal with leading tabs.
+
+        Example:
+
+        >>> d = Differ()
+        >>> results = d._qformat('\tabcDefghiJkl\n', '\t\tabcdefGhijkl\n',
+        ...                      '  ^ ^  ^      ', '+  ^ ^  ^      ')
+        >>> for line in results: print repr(line)
+        ...
+        '- \tabcDefghiJkl\n'
+        '? \t ^ ^  ^\n'
+        '+ \t\tabcdefGhijkl\n'
+        '? \t  ^ ^  ^\n'
+        """
+
+        # Can hurt, but will probably help most of the time.
+        common = min(_count_leading(aline, "\t"),
+                     _count_leading(bline, "\t"))
+        common = min(common, _count_leading(atags[:common], " "))
+        atags = atags[common:].rstrip()
+        btags = btags[common:].rstrip()
+
+        yield "- " + aline
+        if atags:
+            yield "? %s%s\n" % ("\t" * common, atags)
+
+        yield "+ " + bline
+        if btags:
+            yield "? %s%s\n" % ("\t" * common, btags)
+
+# With respect to junk, an earlier version of ndiff simply refused to
+# *start* a match with a junk element.  The result was cases like this:
+#     before: private Thread currentThread;
+#     after:  private volatile Thread currentThread;
+# If you consider whitespace to be junk, the longest contiguous match
+# not starting with junk is "e Thread currentThread".  So ndiff reported
+# that "e volatil" was inserted between the 't' and the 'e' in "private".
+# While an accurate view, to people that's absurd.  The current version
+# looks for matching blocks that are entirely junk-free, then extends the
+# longest one of those as far as possible but only with matching junk.
+# So now "currentThread" is matched, then extended to suck up the
+# preceding blank; then "private" is matched, and extended to suck up the
+# following blank; then "Thread" is matched; and finally ndiff reports
+# that "volatile " was inserted before "Thread".  The only quibble
+# remaining is that perhaps it was really the case that " volatile"
+# was inserted after "private".  I can live with that <wink>.
+
+import re
+
+def IS_LINE_JUNK(line, pat=re.compile(r"\s*#?\s*$").match):
+    r"""
+    Return 1 for ignorable line: iff `line` is blank or contains a single '#'.
+
+    Examples:
+
+    >>> IS_LINE_JUNK('\n')
+    True
+    >>> IS_LINE_JUNK('  #   \n')
+    True
+    >>> IS_LINE_JUNK('hello\n')
+    False
+    """
+
+    return pat(line) is not None
+
+def IS_CHARACTER_JUNK(ch, ws=" \t"):
+    r"""
+    Return 1 for ignorable character: iff `ch` is a space or tab.
+
+    Examples:
+
+    >>> IS_CHARACTER_JUNK(' ')
+    True
+    >>> IS_CHARACTER_JUNK('\t')
+    True
+    >>> IS_CHARACTER_JUNK('\n')
+    False
+    >>> IS_CHARACTER_JUNK('x')
+    False
+    """
+
+    return ch in ws
+
+
+def unified_diff(a, b, fromfile='', tofile='', fromfiledate='',
+                 tofiledate='', n=3, lineterm='\n'):
+    r"""
+    Compare two sequences of lines; generate the delta as a unified diff.
+
+    Unified diffs are a compact way of showing line changes and a few
+    lines of context.  The number of context lines is set by 'n' which
+    defaults to three.
+
+    By default, the diff control lines (those with ---, +++, or @@) are
+    created with a trailing newline.  This is helpful so that inputs
+    created from file.readlines() result in diffs that are suitable for
+    file.writelines() since both the inputs and outputs have trailing
+    newlines.
+
+    For inputs that do not have trailing newlines, set the lineterm
+    argument to "" so that the output will be uniformly newline free.
+
+    The unidiff format normally has a header for filenames and modification
+    times.  Any or all of these may be specified using strings for
+    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.  The modification
+    times are normally expressed in the format returned by time.ctime().
+
+    Example:
+
+    >>> for line in unified_diff('one two three four'.split(),
+    ...             'zero one tree four'.split(), 'Original', 'Current',
+    ...             'Sat Jan 26 23:30:50 1991', 'Fri Jun 06 10:20:52 2003',
+    ...             lineterm=''):
+    ...     print line
+    --- Original Sat Jan 26 23:30:50 1991
+    +++ Current Fri Jun 06 10:20:52 2003
+    @@ -1,4 +1,4 @@
+    +zero
+     one
+    -two
+    -three
+    +tree
+     four
+    """
+
+    started = False
+    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
+        if not started:
+            yield '--- %s %s%s' % (fromfile, fromfiledate, lineterm)
+            yield '+++ %s %s%s' % (tofile, tofiledate, lineterm)
+            started = True
+        i1, i2, j1, j2 = group[0][1], group[-1][2], group[0][3], group[-1][4]
+        yield "@@ -%d,%d +%d,%d @@%s" % (i1+1, i2-i1, j1+1, j2-j1, lineterm)
+        for tag, i1, i2, j1, j2 in group:
+            if tag == 'equal':
+                for line in a[i1:i2]:
+                    yield ' ' + line
+                continue
+            if tag == 'replace' or tag == 'delete':
+                for line in a[i1:i2]:
+                    yield '-' + line
+            if tag == 'replace' or tag == 'insert':
+                for line in b[j1:j2]:
+                    yield '+' + line
+
+# See http://www.unix.org/single_unix_specification/
+def context_diff(a, b, fromfile='', tofile='',
+                 fromfiledate='', tofiledate='', n=3, lineterm='\n'):
+    r"""
+    Compare two sequences of lines; generate the delta as a context diff.
+
+    Context diffs are a compact way of showing line changes and a few
+    lines of context.  The number of context lines is set by 'n' which
+    defaults to three.
+
+    By default, the diff control lines (those with *** or ---) are
+    created with a trailing newline.  This is helpful so that inputs
+    created from file.readlines() result in diffs that are suitable for
+    file.writelines() since both the inputs and outputs have trailing
+    newlines.
+
+    For inputs that do not have trailing newlines, set the lineterm
+    argument to "" so that the output will be uniformly newline free.
+
+    The context diff format normally has a header for filenames and
+    modification times.  Any or all of these may be specified using
+    strings for 'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
+    The modification times are normally expressed in the format returned
+    by time.ctime().  If not specified, the strings default to blanks.
+
+    Example:
+
+    >>> print ''.join(context_diff('one\ntwo\nthree\nfour\n'.splitlines(1),
+    ...       'zero\none\ntree\nfour\n'.splitlines(1), 'Original', 'Current',
+    ...       'Sat Jan 26 23:30:50 1991', 'Fri Jun 06 10:22:46 2003')),
+    *** Original Sat Jan 26 23:30:50 1991
+    --- Current Fri Jun 06 10:22:46 2003
+    ***************
+    *** 1,4 ****
+      one
+    ! two
+    ! three
+      four
+    --- 1,4 ----
+    + zero
+      one
+    ! tree
+      four
+    """
+
+    started = False
+    prefixmap = {'insert':'+ ', 'delete':'- ', 'replace':'! ', 'equal':'  '}
+    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
+        if not started:
+            yield '*** %s %s%s' % (fromfile, fromfiledate, lineterm)
+            yield '--- %s %s%s' % (tofile, tofiledate, lineterm)
+            started = True
+
+        yield '***************%s' % (lineterm,)
+        if group[-1][2] - group[0][1] >= 2:
+            yield '*** %d,%d ****%s' % (group[0][1]+1, group[-1][2], lineterm)
+        else:
+            yield '*** %d ****%s' % (group[-1][2], lineterm)
+        visiblechanges = [e for e in group if e[0] in ('replace', 'delete')]
+        if visiblechanges:
+            for tag, i1, i2, _, _ in group:
+                if tag != 'insert':
+                    for line in a[i1:i2]:
+                        yield prefixmap[tag] + line
+
+        if group[-1][4] - group[0][3] >= 2:
+            yield '--- %d,%d ----%s' % (group[0][3]+1, group[-1][4], lineterm)
+        else:
+            yield '--- %d ----%s' % (group[-1][4], lineterm)
+        visiblechanges = [e for e in group if e[0] in ('replace', 'insert')]
+        if visiblechanges:
+            for tag, _, _, j1, j2 in group:
+                if tag != 'delete':
+                    for line in b[j1:j2]:
+                        yield prefixmap[tag] + line
+
+def ndiff(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK):
+    r"""
+    Compare `a` and `b` (lists of strings); return a `Differ`-style delta.
+
+    Optional keyword parameters `linejunk` and `charjunk` are for filter
+    functions (or None):
+
+    - linejunk: A function that should accept a single string argument, and
+      return true iff the string is junk.  The default is None, and is
+      recommended; as of Python 2.3, an adaptive notion of "noise" lines is
+      used that does a good job on its own.
+
+    - charjunk: A function that should accept a string of length 1. The
+      default is module-level function IS_CHARACTER_JUNK, which filters out
+      whitespace characters (a blank or tab; note: bad idea to include newline
+      in this!).
+
+    Tools/scripts/ndiff.py is a command-line front-end to this function.
+
+    Example:
+
+    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
+    ...              'ore\ntree\nemu\n'.splitlines(1))
+    >>> print ''.join(diff),
+    - one
+    ?  ^
+    + ore
+    ?  ^
+    - two
+    - three
+    ?  -
+    + tree
+    + emu
+    """
+    return Differ(linejunk, charjunk).compare(a, b)
+
+def _mdiff(fromlines, tolines, context=None, linejunk=None,
+           charjunk=IS_CHARACTER_JUNK):
+    """Returns generator yielding marked up from/to side by side differences.
+
+    Arguments:
+    fromlines -- list of text lines to compared to tolines
+    tolines -- list of text lines to be compared to fromlines
+    context -- number of context lines to display on each side of difference,
+               if None, all from/to text lines will be generated.
+    linejunk -- passed on to ndiff (see ndiff documentation)
+    charjunk -- passed on to ndiff (see ndiff documentation)
+
+    This function returns an interator which returns a tuple:
+    (from line tuple, to line tuple, boolean flag)
+
+    from/to line tuple -- (line num, line text)
+        line num -- integer or None (to indicate a context seperation)
+        line text -- original line text with following markers inserted:
+            '\0+' -- marks start of added text
+            '\0-' -- marks start of deleted text
+            '\0^' -- marks start of changed text
+            '\1' -- marks end of added/deleted/changed text
+
+    boolean flag -- None indicates context separation, True indicates
+        either "from" or "to" line contains a change, otherwise False.
+
+    This function/iterator was originally developed to generate side by side
+    file difference for making HTML pages (see HtmlDiff class for example
+    usage).
+
+    Note, this function utilizes the ndiff function to generate the side by
+    side difference markup.  Optional ndiff arguments may be passed to this
+    function and they in turn will be passed to ndiff.
+    """
+    import re
+
+    # regular expression for finding intraline change indices
+    change_re = re.compile('(\++|\-+|\^+)')
+
+    # create the difference iterator to generate the differences
+    diff_lines_iterator = ndiff(fromlines,tolines,linejunk,charjunk)
+
+    def _make_line(lines, format_key, side, num_lines=[0,0]):
+        """Returns line of text with user's change markup and line formatting.
+
+        lines -- list of lines from the ndiff generator to produce a line of
+                 text from.  When producing the line of text to return, the
+                 lines used are removed from this list.
+        format_key -- '+' return first line in list with "add" markup around
+                          the entire line.
+                      '-' return first line in list with "delete" markup around
+                          the entire line.
+                      '?' return first line in list with add/delete/change
+                          intraline markup (indices obtained from second line)
+                      None return first line in list with no markup
+        side -- indice into the num_lines list (0=from,1=to)
+        num_lines -- from/to current line number.  This is NOT intended to be a
+                     passed parameter.  It is present as a keyword argument to
+                     maintain memory of the current line numbers between calls
+                     of this function.
+
+        Note, this function is purposefully not defined at the module scope so
+        that data it needs from its parent function (within whose context it
+        is defined) does not need to be of module scope.
+        """
+        num_lines[side] += 1
+        # Handle case where no user markup is to be added, just return line of
+        # text with user's line format to allow for usage of the line number.
+        if format_key is None:
+            return (num_lines[side],lines.pop(0)[2:])
+        # Handle case of intraline changes
+        if format_key == '?':
+            text, markers = lines.pop(0), lines.pop(0)
+            # find intraline changes (store change type and indices in tuples)
+            sub_info = []
+            def record_sub_info(match_object,sub_info=sub_info):
+                sub_info.append([match_object.group(1)[0],match_object.span()])
+                return match_object.group(1)
+            change_re.sub(record_sub_info,markers)
+            # process each tuple inserting our special marks that won't be
+            # noticed by an xml/html escaper.
+            for key,(begin,end) in sub_info[::-1]:
+                text = text[0:begin]+'\0'+key+text[begin:end]+'\1'+text[end:]
+            text = text[2:]
+        # Handle case of add/delete entire line
+        else:
+            text = lines.pop(0)[2:]
+            # if line of text is just a newline, insert a space so there is
+            # something for the user to highlight and see.
+            if not text:
+                text = ' '
+            # insert marks that won't be noticed by an xml/html escaper.
+            text = '\0' + format_key + text + '\1'
+        # Return line of text, first allow user's line formatter to do its
+        # thing (such as adding the line number) then replace the special
+        # marks with what the user's change markup.
+        return (num_lines[side],text)
+
+    def _line_iterator():
+        """Yields from/to lines of text with a change indication.
+
+        This function is an iterator.  It itself pulls lines from a
+        differencing iterator, processes them and yields them.  When it can
+        it yields both a "from" and a "to" line, otherwise it will yield one
+        or the other.  In addition to yielding the lines of from/to text, a
+        boolean flag is yielded to indicate if the text line(s) have
+        differences in them.
+
+        Note, this function is purposefully not defined at the module scope so
+        that data it needs from its parent function (within whose context it
+        is defined) does not need to be of module scope.
+        """
+        lines = []
+        num_blanks_pending, num_blanks_to_yield = 0, 0
+        while True:
+            # Load up next 4 lines so we can look ahead, create strings which
+            # are a concatenation of the first character of each of the 4 lines
+            # so we can do some very readable comparisons.
+            while len(lines) < 4:
+                try:
+                    lines.append(diff_lines_iterator.next())
+                except StopIteration:
+                    lines.append('X')
+            s = ''.join([line[0] for line in lines])
+            if s.startswith('X'):
+                # When no more lines, pump out any remaining blank lines so the
+                # corresponding add/delete lines get a matching blank line so
+                # all line pairs get yielded at the next level.
+                num_blanks_to_yield = num_blanks_pending
+            elif s.startswith('-?+?'):
+                # simple intraline change
+                yield _make_line(lines,'?',0), _make_line(lines,'?',1), True
+                continue
+            elif s.startswith('--++'):
+                # in delete block, add block coming: we do NOT want to get
+                # caught up on blank lines yet, just process the delete line
+                num_blanks_pending -= 1
+                yield _make_line(lines,'-',0), None, True
+                continue
+            elif s.startswith(('--?+', '--+', '- ')):
+                # in delete block and see a intraline change or unchanged line
+                # coming: yield the delete line and then blanks
+                from_line,to_line = _make_line(lines,'-',0), None
+                num_blanks_to_yield,num_blanks_pending = num_blanks_pending-1,0
+            elif s.startswith('-+?'):
+                # intraline change
+                yield _make_line(lines,None,0), _make_line(lines,'?',1), True
+                continue
+            elif s.startswith('-?+'):
+                # intraline change
+                yield _make_line(lines,'?',0), _make_line(lines,None,1), True
+                continue
+            elif s.startswith('-'):
+                # delete FROM line
+                num_blanks_pending -= 1
+                yield _make_line(lines,'-',0), None, True
+                continue
+            elif s.startswith('+--'):
+                # in add block, delete block coming: we do NOT want to get
+                # caught up on blank lines yet, just process the add line
+                num_blanks_pending += 1
+                yield None, _make_line(lines,'+',1), True
+                continue
+            elif s.startswith(('+ ', '+-')):
+                # will be leaving an add block: yield blanks then add line
+                from_line, to_line = None, _make_line(lines,'+',1)
+                num_blanks_to_yield,num_blanks_pending = num_blanks_pending+1,0
+            elif s.startswith('+'):
+                # inside an add block, yield the add line
+                num_blanks_pending += 1
+                yield None, _make_line(lines,'+',1), True
+                continue
+            elif s.startswith(' '):
+                # unchanged text, yield it to both sides
+                yield _make_line(lines[:],None,0),_make_line(lines,None,1),False
+                continue
+            # Catch up on the blank lines so when we yield the next from/to
+            # pair, they are lined up.
+            while(num_blanks_to_yield < 0):
+                num_blanks_to_yield += 1
+                yield None,('','\n'),True
+            while(num_blanks_to_yield > 0):
+                num_blanks_to_yield -= 1
+                yield ('','\n'),None,True
+            if s.startswith('X'):
+                raise StopIteration
+            else:
+                yield from_line,to_line,True
+
+    def _line_pair_iterator():
+        """Yields from/to lines of text with a change indication.
+
+        This function is an iterator.  It itself pulls lines from the line
+        iterator.  Its difference from that iterator is that this function
+        always yields a pair of from/to text lines (with the change
+        indication).  If necessary it will collect single from/to lines
+        until it has a matching pair from/to pair to yield.
+
+        Note, this function is purposefully not defined at the module scope so
+        that data it needs from its parent function (within whose context it
+        is defined) does not need to be of module scope.
+        """
+        line_iterator = _line_iterator()
+        fromlines,tolines=[],[]
+        while True:
+            # Collecting lines of text until we have a from/to pair
+            while (len(fromlines)==0 or len(tolines)==0):
+                from_line, to_line, found_diff =line_iterator.next()
+                if from_line is not None:
+                    fromlines.append((from_line,found_diff))
+                if to_line is not None:
+                    tolines.append((to_line,found_diff))
+            # Once we have a pair, remove them from the collection and yield it
+            from_line, fromDiff = fromlines.pop(0)
+            to_line, to_diff = tolines.pop(0)
+            yield (from_line,to_line,fromDiff or to_diff)
+
+    # Handle case where user does not want context differencing, just yield
+    # them up without doing anything else with them.
+    line_pair_iterator = _line_pair_iterator()
+    if context is None:
+        while True:
+            yield line_pair_iterator.next()
+    # Handle case where user wants context differencing.  We must do some
+    # storage of lines until we know for sure that they are to be yielded.
+    else:
+        context += 1
+        lines_to_write = 0
+        while True:
+            # Store lines up until we find a difference, note use of a
+            # circular queue because we only need to keep around what
+            # we need for context.
+            index, contextLines = 0, [None]*(context)
+            found_diff = False
+            while(found_diff is False):
+                from_line, to_line, found_diff = line_pair_iterator.next()
+                i = index % context
+                contextLines[i] = (from_line, to_line, found_diff)
+                index += 1
+            # Yield lines that we have collected so far, but first yield
+            # the user's separator.
+            if index > context:
+                yield None, None, None
+                lines_to_write = context
+            else:
+                lines_to_write = index
+                index = 0
+            while(lines_to_write):
+                i = index % context
+                index += 1
+                yield contextLines[i]
+                lines_to_write -= 1
+            # Now yield the context lines after the change
+            lines_to_write = context-1
+            while(lines_to_write):
+                from_line, to_line, found_diff = line_pair_iterator.next()
+                # If another change within the context, extend the context
+                if found_diff:
+                    lines_to_write = context-1
+                else:
+                    lines_to_write -= 1
+                yield from_line, to_line, found_diff
+
+
+_file_template = """
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+<html>
+
+<head>
+    <meta http-equiv="Content-Type"
+          content="text/html; charset=ISO-8859-1" />
+    <title></title>
+    <style type="text/css">%(styles)s
+    </style>
+</head>
+
+<body>
+    %(table)s%(legend)s
+</body>
+
+</html>"""
+
+_styles = """
+        table.diff {font-family:Courier; border:medium;}
+        .diff_header {background-color:#e0e0e0}
+        td.diff_header {text-align:right}
+        .diff_next {background-color:#c0c0c0}
+        .diff_add {background-color:#aaffaa}
+        .diff_chg {background-color:#ffff77}
+        .diff_sub {background-color:#ffaaaa}"""
+
+_table_template = """
+    <table class="diff" id="difflib_chg_%(prefix)s_top"
+           cellspacing="0" cellpadding="0" rules="groups" >
+        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
+        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
+        %(header_row)s
+        <tbody>
+%(data_rows)s        </tbody>
+    </table>"""
+
+_legend = """
+    <table class="diff" summary="Legends">
+        <tr> <th colspan="2"> Legends </th> </tr>
+        <tr> <td> <table border="" summary="Colors">
+                      <tr><th> Colors </th> </tr>
+                      <tr><td class="diff_add">&nbsp;Added&nbsp;</td></tr>
+                      <tr><td class="diff_chg">Changed</td> </tr>
+                      <tr><td class="diff_sub">Deleted</td> </tr>
+                  </table></td>
+             <td> <table border="" summary="Links">
+                      <tr><th colspan="2"> Links </th> </tr>
+                      <tr><td>(f)irst change</td> </tr>
+                      <tr><td>(n)ext change</td> </tr>
+                      <tr><td>(t)op</td> </tr>
+                  </table></td> </tr>
+    </table>"""
+
+class HtmlDiff(object):
+    """For producing HTML side by side comparison with change highlights.
+
+    This class can be used to create an HTML table (or a complete HTML file
+    containing the table) showing a side by side, line by line comparison
+    of text with inter-line and intra-line change highlights.  The table can
+    be generated in either full or contextual difference mode.
+
+    The following methods are provided for HTML generation:
+
+    make_table -- generates HTML for a single side by side table
+    make_file -- generates complete HTML file with a single side by side table
+
+    See tools/scripts/diff.py for an example usage of this class.
+    """
+
+    _file_template = _file_template
+    _styles = _styles
+    _table_template = _table_template
+    _legend = _legend
+    _default_prefix = 0
+
+    def __init__(self,tabsize=8,wrapcolumn=None,linejunk=None,
+                 charjunk=IS_CHARACTER_JUNK):
+        """HtmlDiff instance initializer
+
+        Arguments:
+        tabsize -- tab stop spacing, defaults to 8.
+        wrapcolumn -- column number where lines are broken and wrapped,
+            defaults to None where lines are not wrapped.
+        linejunk,charjunk -- keyword arguments passed into ndiff() (used to by
+            HtmlDiff() to generate the side by side HTML differences).  See
+            ndiff() documentation for argument default values and descriptions.
+        """
+        self._tabsize = tabsize
+        self._wrapcolumn = wrapcolumn
+        self._linejunk = linejunk
+        self._charjunk = charjunk
+
+    def make_file(self,fromlines,tolines,fromdesc='',todesc='',context=False,
+                  numlines=5):
+        """Returns HTML file of side by side comparison with change highlights
+
+        Arguments:
+        fromlines -- list of "from" lines
+        tolines -- list of "to" lines
+        fromdesc -- "from" file column header string
+        todesc -- "to" file column header string
+        context -- set to True for contextual differences (defaults to False
+            which shows full differences).
+        numlines -- number of context lines.  When context is set True,
+            controls number of lines displayed before and after the change.
+            When context is False, controls the number of lines to place
+            the "next" link anchors before the next change (so click of
+            "next" link jumps to just before the change).
+        """
+
+        return self._file_template % dict(
+            styles = self._styles,
+            legend = self._legend,
+            table = self.make_table(fromlines,tolines,fromdesc,todesc,
+                                    context=context,numlines=numlines))
+
+    def _tab_newline_replace(self,fromlines,tolines):
+        """Returns from/to line lists with tabs expanded and newlines removed.
+
+        Instead of tab characters being replaced by the number of spaces
+        needed to fill in to the next tab stop, this function will fill
+        the space with tab characters.  This is done so that the difference
+        algorithms can identify changes in a file when tabs are replaced by
+        spaces and vice versa.  At the end of the HTML generation, the tab
+        characters will be replaced with a nonbreakable space.
+        """
+        def expand_tabs(line):
+            # hide real spaces
+            line = line.replace(' ','\0')
+            # expand tabs into spaces
+            line = line.expandtabs(self._tabsize)
+            # relace spaces from expanded tabs back into tab characters
+            # (we'll replace them with markup after we do differencing)
+            line = line.replace(' ','\t')
+            return line.replace('\0',' ').rstrip('\n')
+        fromlines = [expand_tabs(line) for line in fromlines]
+        tolines = [expand_tabs(line) for line in tolines]
+        return fromlines,tolines
+
+    def _split_line(self,data_list,line_num,text):
+        """Builds list of text lines by splitting text lines at wrap point
+
+        This function will determine if the input text line needs to be
+        wrapped (split) into separate lines.  If so, the first wrap point
+        will be determined and the first line appended to the output
+        text line list.  This function is used recursively to handle
+        the second part of the split line to further split it.
+        """
+        # if blank line or context separator, just add it to the output list
+        if not line_num:
+            data_list.append((line_num,text))
+            return
+
+        # if line text doesn't need wrapping, just add it to the output list
+        size = len(text)
+        max = self._wrapcolumn
+        if (size <= max) or ((size -(text.count('\0')*3)) <= max):
+            data_list.append((line_num,text))
+            return
+
+        # scan text looking for the wrap point, keeping track if the wrap
+        # point is inside markers
+        i = 0
+        n = 0
+        mark = ''
+        while n < max and i < size:
+            if text[i] == '\0':
+                i += 1
+                mark = text[i]
+                i += 1
+            elif text[i] == '\1':
+                i += 1
+                mark = ''
+            else:
+                i += 1
+                n += 1
+
+        # wrap point is inside text, break it up into separate lines
+        line1 = text[:i]
+        line2 = text[i:]
+
+        # if wrap point is inside markers, place end marker at end of first
+        # line and start marker at beginning of second line because each
+        # line will have its own table tag markup around it.
+        if mark:
+            line1 = line1 + '\1'
+            line2 = '\0' + mark + line2
+
+        # tack on first line onto the output list
+        data_list.append((line_num,line1))
+
+        # use this routine again to wrap the remaining text
+        self._split_line(data_list,'>',line2)
+
+    def _line_wrapper(self,diffs):
+        """Returns iterator that splits (wraps) mdiff text lines"""
+
+        # pull from/to data and flags from mdiff iterator
+        for fromdata,todata,flag in diffs:
+            # check for context separators and pass them through
+            if flag is None:
+                yield fromdata,todata,flag
+                continue
+            (fromline,fromtext),(toline,totext) = fromdata,todata
+            # for each from/to line split it at the wrap column to form
+            # list of text lines.
+            fromlist,tolist = [],[]
+            self._split_line(fromlist,fromline,fromtext)
+            self._split_line(tolist,toline,totext)
+            # yield from/to line in pairs inserting blank lines as
+            # necessary when one side has more wrapped lines
+            while fromlist or tolist:
+                if fromlist:
+                    fromdata = fromlist.pop(0)
+                else:
+                    fromdata = ('',' ')
+                if tolist:
+                    todata = tolist.pop(0)
+                else:
+                    todata = ('',' ')
+                yield fromdata,todata,flag
+
+    def _collect_lines(self,diffs):
+        """Collects mdiff output into separate lists
+
+        Before storing the mdiff from/to data into a list, it is converted
+        into a single line of text with HTML markup.
+        """
+
+        fromlist,tolist,flaglist = [],[],[]
+        # pull from/to data and flags from mdiff style iterator
+        for fromdata,todata,flag in diffs:
+            try:
+                # store HTML markup of the lines into the lists
+                fromlist.append(self._format_line(0,flag,*fromdata))
+                tolist.append(self._format_line(1,flag,*todata))
+            except TypeError:
+                # exceptions occur for lines where context separators go
+                fromlist.append(None)
+                tolist.append(None)
+            flaglist.append(flag)
+        return fromlist,tolist,flaglist
+
+    def _format_line(self,side,flag,linenum,text):
+        """Returns HTML markup of "from" / "to" text lines
+
+        side -- 0 or 1 indicating "from" or "to" text
+        flag -- indicates if difference on line
+        linenum -- line number (used for line number column)
+        text -- line text to be marked up
+        """
+        try:
+            linenum = '%d' % linenum
+            id = ' id="%s%s"' % (self._prefix[side],linenum)
+        except TypeError:
+            # handle blank lines where linenum is '>' or ''
+            id = ''
+        # replace those things that would get confused with HTML symbols
+        text=text.replace("&","&amp;").replace(">","&gt;").replace("<","&lt;")
+
+        # make space non-breakable so they don't get compressed or line wrapped
+        text = text.replace(' ','&nbsp;').rstrip()
+
+        return '<td class="diff_header"%s>%s</td><td nowrap="nowrap">%s</td>' \
+               % (id,linenum,text)
+
+    def _make_prefix(self):
+        """Create unique anchor prefixes"""
+
+        # Generate a unique anchor prefix so multiple tables
+        # can exist on the same HTML page without conflicts.
+        fromprefix = "from%d_" % HtmlDiff._default_prefix
+        toprefix = "to%d_" % HtmlDiff._default_prefix
+        HtmlDiff._default_prefix += 1
+        # store prefixes so line format method has access
+        self._prefix = [fromprefix,toprefix]
+
+    def _convert_flags(self,fromlist,tolist,flaglist,context,numlines):
+        """Makes list of "next" links"""
+
+        # all anchor names will be generated using the unique "to" prefix
+        toprefix = self._prefix[1]
+
+        # process change flags, generating middle column of next anchors/links
+        next_id = ['']*len(flaglist)
+        next_href = ['']*len(flaglist)
+        num_chg, in_change = 0, False
+        last = 0
+        for i,flag in enumerate(flaglist):
+            if flag:
+                if not in_change:
+                    in_change = True
+                    last = i
+                    # at the beginning of a change, drop an anchor a few lines
+                    # (the context lines) before the change for the previous
+                    # link
+                    i = max([0,i-numlines])
+                    next_id[i] = ' id="difflib_chg_%s_%d"' % (toprefix,num_chg)
+                    # at the beginning of a change, drop a link to the next
+                    # change
+                    num_chg += 1
+                    next_href[last] = '<a href="#difflib_chg_%s_%d">n</a>' % (
+                         toprefix,num_chg)
+            else:
+                in_change = False
+        # check for cases where there is no content to avoid exceptions
+        if not flaglist:
+            flaglist = [False]
+            next_id = ['']
+            next_href = ['']
+            last = 0
+            if context:
+                fromlist = ['<td></td><td>&nbsp;No Differences Found&nbsp;</td>']
+                tolist = fromlist
+            else:
+                fromlist = tolist = ['<td></td><td>&nbsp;Empty File&nbsp;</td>']
+        # if not a change on first line, drop a link
+        if not flaglist[0]:
+            next_href[0] = '<a href="#difflib_chg_%s_0">f</a>' % toprefix
+        # redo the last link to link to the top
+        next_href[last] = '<a href="#difflib_chg_%s_top">t</a>' % (toprefix)
+
+        return fromlist,tolist,flaglist,next_href,next_id
+
+    def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
+                   numlines=5):
+        """Returns HTML table of side by side comparison with change highlights
+
+        Arguments:
+        fromlines -- list of "from" lines
+        tolines -- list of "to" lines
+        fromdesc -- "from" file column header string
+        todesc -- "to" file column header string
+        context -- set to True for contextual differences (defaults to False
+            which shows full differences).
+        numlines -- number of context lines.  When context is set True,
+            controls number of lines displayed before and after the change.
+            When context is False, controls the number of lines to place
+            the "next" link anchors before the next change (so click of
+            "next" link jumps to just before the change).
+        """
+
+        # make unique anchor prefixes so that multiple tables may exist
+        # on the same page without conflict.
+        self._make_prefix()
+
+        # change tabs to spaces before it gets more difficult after we insert
+        # markkup
+        fromlines,tolines = self._tab_newline_replace(fromlines,tolines)
+
+        # create diffs iterator which generates side by side from/to data
+        if context:
+            context_lines = numlines
+        else:
+            context_lines = None
+        diffs = _mdiff(fromlines,tolines,context_lines,linejunk=self._linejunk,
+                      charjunk=self._charjunk)
+
+        # set up iterator to wrap lines that exceed desired width
+        if self._wrapcolumn:
+            diffs = self._line_wrapper(diffs)
+
+        # collect up from/to lines and flags into lists (also format the lines)
+        fromlist,tolist,flaglist = self._collect_lines(diffs)
+
+        # process change flags, generating middle column of next anchors/links
+        fromlist,tolist,flaglist,next_href,next_id = self._convert_flags(
+            fromlist,tolist,flaglist,context,numlines)
+
+        import cStringIO
+        s = cStringIO.StringIO()
+        fmt = '            <tr><td class="diff_next"%s>%s</td>%s' + \
+              '<td class="diff_next">%s</td>%s</tr>\n'
+        for i in range(len(flaglist)):
+            if flaglist[i] is None:
+                # mdiff yields None on separator lines skip the bogus ones
+                # generated for the first line
+                if i > 0:
+                    s.write('        </tbody>        \n        <tbody>\n')
+            else:
+                s.write( fmt % (next_id[i],next_href[i],fromlist[i],
+                                           next_href[i],tolist[i]))
+        if fromdesc or todesc:
+            header_row = '<thead><tr>%s%s%s%s</tr></thead>' % (
+                '<th class="diff_next"><br /></th>',
+                '<th colspan="2" class="diff_header">%s</th>' % fromdesc,
+                '<th class="diff_next"><br /></th>',
+                '<th colspan="2" class="diff_header">%s</th>' % todesc)
+        else:
+            header_row = ''
+
+        table = self._table_template % dict(
+            data_rows=s.getvalue(),
+            header_row=header_row,
+            prefix=self._prefix[1])
+
+        return table.replace('\0+','<span class="diff_add">'). \
+                     replace('\0-','<span class="diff_sub">'). \
+                     replace('\0^','<span class="diff_chg">'). \
+                     replace('\1','</span>'). \
+                     replace('\t','&nbsp;')
+
+del re
+
+def restore(delta, which):
+    r"""
+    Generate one of the two sequences that generated a delta.
+
+    Given a `delta` produced by `Differ.compare()` or `ndiff()`, extract
+    lines originating from file 1 or 2 (parameter `which`), stripping off line
+    prefixes.
+
+    Examples:
+
+    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
+    ...              'ore\ntree\nemu\n'.splitlines(1))
+    >>> diff = list(diff)
+    >>> print ''.join(restore(diff, 1)),
+    one
+    two
+    three
+    >>> print ''.join(restore(diff, 2)),
+    ore
+    tree
+    emu
+    """
+    try:
+        tag = {1: "- ", 2: "+ "}[int(which)]
+    except KeyError:
+        raise ValueError, ('unknown delta choice (must be 1 or 2): %r'
+                           % which)
+    prefixes = ("  ", tag)
+    for line in delta:
+        if line[:2] in prefixes:
+            yield line[2:]
+
+def _test():
+    import doctest, difflib
+    return doctest.testmod(difflib)
+
+if __name__ == "__main__":
+    _test()
--- a/MoinMoin/util/diff.py	Sat Jun 24 20:43:47 2006 +0200
+++ b/MoinMoin/util/diff.py	Sun Jun 25 14:41:11 2006 +0200
@@ -7,7 +7,7 @@
     @license: GNU GPL, see COPYING for details.
 """
 
-import difflib
+from MoinMoin.support import difflib
 from MoinMoin.wikiutil import escape
 
 def indent(line):
--- a/MoinMoin/wikiutil.py	Sat Jun 24 20:43:47 2006 +0200
+++ b/MoinMoin/wikiutil.py	Sun Jun 25 14:41:11 2006 +0200
@@ -6,9 +6,10 @@
     @license: GNU GPL, see COPYING for details.
 """
     
-import os, re, difflib, urllib, cgi
+import os, re, urllib, cgi
 import codecs, types
 
+from MoinMoin.support import difflib
 from MoinMoin import util, version, config
 from MoinMoin.util import pysupport, filesys
 
--- a/docs/CHANGES	Sat Jun 24 20:43:47 2006 +0200
+++ b/docs/CHANGES	Sun Jun 25 14:41:11 2006 +0200
@@ -172,6 +172,7 @@
     * fixed MoinMoin:MoinMoinBugs/GuiEditorDeletesNewBulletText
     * fixed MoinMoin:MoinMoinBugs/HtmlTextConvertTables
     * updated ImageLink macro
+    * Added a (less broken) MoinMoin.support.difflib, details see there.
 
   Other changes:
     * we use (again) the same browser compatibility check as FCKeditor uses