Replace ndiff.py with stdlib's difflib

2 files changed, 2 insertions, 673 deletions

diff --git a/src/zope/tal/ndiff.py b/src/zope/tal/ndiff.py
deleted file mode 100644
index 036b138..0000000
--- a/src/zope/tal/ndiff.py
+++ /dev/null
@@ -1,657 +0,0 @@
-#! /usr/bin/env python
-##############################################################################
-#
-# Copyright (c) 2001, 2002 Zope Foundation and Contributors.
-# All Rights Reserved.
-#
-# This software is subject to the provisions of the Zope Public License,
-# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
-# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
-# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
-# FOR A PARTICULAR PURPOSE.
-#
-##############################################################################
-
-# Module ndiff version 1.6.0
-# Released to the public domain 08-Dec-2000,
-# by Tim Peters (tim.one@home.com).
-
-# Provided as-is; use at your own risk; no warranty; no promises; enjoy!
-
-"""ndiff [-q] file1 file2
-    or
-ndiff (-r1 | -r2) < ndiff_output > file1_or_file2
-
-Print a human-friendly file difference report to stdout.  Both inter-
-and intra-line differences are noted.  In the second form, recreate file1
-(-r1) or file2 (-r2) on stdout, from an ndiff report on stdin.
-
-In the first form, if -q ("quiet") is not specified, the first two lines
-of output are
-
--: file1
-+: file2
-
-Each remaining line begins with a two-letter code:
-
-    "- "    line unique to file1
-    "+ "    line unique to file2
-    "  "    line common to both files
-    "? "    line not present in either input file
-
-Lines beginning with "? " attempt to guide the eye to intraline
-differences, and were not present in either input file.  These lines can be
-confusing if the source files contain tab characters.
-
-The first file can be recovered by retaining only lines that begin with
-"  " or "- ", and deleting those 2-character prefixes; use ndiff with -r1.
-
-The second file can be recovered similarly, but by retaining only "  " and
-"+ " lines; use ndiff with -r2; or, on Unix, the second file can be
-recovered by piping the output through
-
-    sed -n '/^[+ ] /s/^..//p'
-
-See module comments for details and programmatic interface.
-"""
-
-from __future__ import print_function
-from functools import reduce
-
-
-try:
-    xrange
-except NameError:
-    xrange = range # Python 3.x
-
-
-__version__ = 1, 5, 0
-
-# SequenceMatcher tries to compute a "human-friendly diff" between
-# two sequences (chiefly picturing a file as a sequence of lines,
-# and a line as a sequence of characters, here).  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>.
-#
-# Note that ndiff 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.
-#
-# 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>.
-#
-# NOTE on junk:  the module-level names
-#    IS_LINE_JUNK
-#    IS_CHARACTER_JUNK
-# can be set to any functions you like.  The first one should accept
-# a single string argument, and return true iff the string is junk.
-# The default is whether the regexp r"\s*#?\s*$" matches (i.e., a
-# line without visible characters, except for at most one splat).
-# The second should accept a string of length 1 etc.  The default is
-# whether the character is a blank or tab (note: bad idea to include
-# newline in this!).
-#
-# After setting those, you can call fcompare(f1name, f2name) with the
-# names of the files you want to compare.  The difference report
-# is sent to stdout.  Or you can call main(args), passing what would
-# have been in sys.argv[1:] had the cmd-line form been used.
-
-TRACE = 0
-
-# define what "junk" means
-import re
-
-def IS_LINE_JUNK(line, pat=re.compile(r"\s*#?\s*$").match):
-    return pat(line) is not None
-
-def IS_CHARACTER_JUNK(ch, ws=" \t"):
-    return ch in ws
-
-del re
-
-class SequenceMatcher(object):
-    def __init__(self, isjunk=None, a='', b=''):
-        # 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
-        # b2jhas
-        #      b2j.has_key
-        # 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!
-
-        self.isjunk = isjunk
-        self.a = self.b = None
-        self.set_seqs(a, b)
-
-    def set_seqs(self, a, b):
-        self.set_seq1(a)
-        self.set_seq2(b)
-
-    def set_seq1(self, a):
-        if a is self.a:
-            return
-        self.a = a
-        self.matching_blocks = self.opcodes = None
-
-    def set_seq2(self, b):
-        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 ...
-    # 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
-        self.b2j = b2j = {}
-        self.b2jhas = b2jhas = b2j.has_key
-        for i in xrange(len(b)):
-            elt = b[i]
-            if b2jhas(elt):
-                b2j[elt].append(i)
-            else:
-                b2j[elt] = [i]
-
-        # 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, junkdict = self.isjunk, {}
-        if isjunk:
-            for elt in list(b2j):
-                if isjunk(elt):
-                    junkdict[elt] = 1   # value irrelevant; it's a set
-                    del b2j[elt]
-
-        # Now for x in b, isjunk(x) == junkdict.has_key(x), 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
-
-    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.
-
-        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.
-
-        If no blocks match, return (alo, blo, 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
-
-        # 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
-
-        if TRACE:
-            print("get_matching_blocks", alo, ahi, blo, bhi)
-            print("    returns", besti, bestj, bestsize)
-        return besti, bestj, bestsize
-
-    def get_matching_blocks(self):
-        if self.matching_blocks is not None:
-            return self.matching_blocks
-        self.matching_blocks = []
-        la, lb = len(self.a), len(self.b)
-        self.__helper(0, la, 0, lb, self.matching_blocks)
-        self.matching_blocks.append((la, lb, 0))
-        if TRACE:
-            print('*** matching blocks', self.matching_blocks)
-        return self.matching_blocks
-
-    # builds list of matching blocks covering a[alo:ahi] and
-    # b[blo:bhi], appending them in increasing order to answer
-
-    def __helper(self, alo, ahi, blo, bhi, answer):
-        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 alo < i and blo < j:
-                self.__helper(alo, i, blo, j, answer)
-            answer.append(x)
-            if i+k < ahi and j+k < bhi:
-                self.__helper(i+k, ahi, j+k, bhi, answer)
-
-    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*M / T.
-        Note that this is 1 if the sequences are identical, and 0 if
-        they have nothing in common.
-        """
-
-        matches = reduce(lambda sum, triple: sum + triple[-1],
-                         self.get_matching_blocks(), 0)
-        return 2.0 * matches / (len(self.a) + len(self.b))
-
-    def quick_ratio(self):
-        """Return an upper bound on ratio() relatively quickly."""
-        # 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 2.0 * matches / (len(self.a) + len(self.b))
-
-    def real_quick_ratio(self):
-        """Return an upper bound on ratio() very quickly"""
-        la, lb = len(self.a), len(self.b)
-        # can't have more matches than the number of elements in the
-        # shorter sequence
-        return 2.0 * min(la, lb) / (la + lb)
-
-    def get_opcodes(self):
-        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
-
-# meant for dumping lines
-def dump(tag, x, lo, hi):
-    for i in xrange(lo, hi):
-        print(tag, x[i], end=' ')
-
-def plain_replace(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:
-        dump('+', b, blo, bhi)
-        dump('-', a, alo, ahi)
-    else:
-        dump('-', a, alo, ahi)
-        dump('+', b, blo, bhi)
-
-# When replacing one block of lines with another, this guy searches
-# 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.
-
-def fancy_replace(a, alo, ahi, b, blo, bhi):
-    if TRACE:
-        print('*** fancy_replace', alo, ahi, blo, bhi)
-        dump('>', a, alo, ahi)
-        dump('<', b, blo, bhi)
-
-    # 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(IS_CHARACTER_JUNK)
-    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
-            plain_replace(a, alo, ahi, b, blo, bhi)
-            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
-    if TRACE:
-        print('*** best_ratio', best_ratio, best_i, best_j)
-        dump('>', a, best_i, best_i+1)
-        dump('<', b, best_j, best_j+1)
-
-    # pump out diffs from before the synch point
-    fancy_helper(a, alo, best_i, b, blo, best_j)
-
-    # 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 = atags + '^' * la
-                btags = btags + '^' * lb
-            elif tag == 'delete':
-                atags = atags + '-' * la
-            elif tag == 'insert':
-                btags = btags + '+' * lb
-            elif tag == 'equal':
-                atags = atags + ' ' * la
-                btags = btags + ' ' * lb
-            else:
-                raise ValueError('unknown tag ' + repr(tag))
-        printq(aelt, belt, atags, btags)
-    else:
-        # the synch pair is identical
-        print(' ', aelt, end=' ')
-
-    # pump out diffs from after the synch point
-    fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi)
-
-def fancy_helper(a, alo, ahi, b, blo, bhi):
-    if alo < ahi:
-        if blo < bhi:
-            fancy_replace(a, alo, ahi, b, blo, bhi)
-        else:
-            dump('-', a, alo, ahi)
-    elif blo < bhi:
-        dump('+', b, blo, bhi)
-
-# Crap to deal with leading tabs in "?" output.  Can hurt, but will
-# probably help most of the time.
-
-def printq(aline, bline, atags, btags):
-    common = min(count_leading(aline, "\t"),
-                 count_leading(bline, "\t"))
-    common = min(common, count_leading(atags[:common], " "))
-    print("-", aline, end=' ')
-    if count_leading(atags, " ") < len(atags):
-        print("?", "\t" * common + atags[common:])
-    print("+", bline, end=' ')
-    if count_leading(btags, " ") < len(btags):
-        print("?", "\t" * common + btags[common:])
-
-def count_leading(line, ch):
-    i, n = 0, len(line)
-    while i < n and line[i] == ch:
-        i = i + 1
-    return i
-
-def fail(msg):
-    import sys
-    out = sys.stderr.write
-    out(msg + "\n\n")
-    out(__doc__)
-    return 0
-
-# open a file & return the file object; gripe and return 0 if it
-# couldn't be opened
-def fopen(fname):
-    try:
-        return open(fname, 'r')
-    except IOError as detail:
-        return fail("couldn't open " + fname + ": " + str(detail))
-
-# open two files & spray the diff to stdout; return false iff a problem
-def fcompare(f1name, f2name):
-    f1 = fopen(f1name)
-    f2 = fopen(f2name)
-    if not f1 or not f2:
-        return 0
-
-    a = f1.readlines(); f1.close()
-    b = f2.readlines(); f2.close()
-
-    cruncher = SequenceMatcher(IS_LINE_JUNK, a, b)
-    for tag, alo, ahi, blo, bhi in cruncher.get_opcodes():
-        if tag == 'replace':
-            fancy_replace(a, alo, ahi, b, blo, bhi)
-        elif tag == 'delete':
-            dump('-', a, alo, ahi)
-        elif tag == 'insert':
-            dump('+', b, blo, bhi)
-        elif tag == 'equal':
-            dump(' ', a, alo, ahi)
-        else:
-            raise ValueError('unknown tag ' + repr(tag))
-
-    return 1
-
-# crack args (sys.argv[1:] is normal) & compare;
-# return false iff a problem
-
-def main(args):
-    import getopt
-    try:
-        opts, args = getopt.getopt(args, "qr:")
-    except getopt.error as detail:
-        return fail(str(detail))
-    noisy = 1
-    qseen = rseen = 0
-    for opt, val in opts:
-        if opt == "-q":
-            qseen = 1
-            noisy = 0
-        elif opt == "-r":
-            rseen = 1
-            whichfile = val
-    if qseen and rseen:
-        return fail("can't specify both -q and -r")
-    if rseen:
-        if args:
-            return fail("no args allowed with -r option")
-        if whichfile in "12":
-            restore(whichfile)
-            return 1
-        return fail("-r value must be 1 or 2")
-    if len(args) != 2:
-        return fail("need 2 filename args")
-    f1name, f2name = args
-    if noisy:
-        print('-:', f1name)
-        print('+:', f2name)
-    return fcompare(f1name, f2name)
-
-def restore(which):
-    import sys
-    tag = {"1": "- ", "2": "+ "}[which]
-    prefixes = ("  ", tag)
-    for line in sys.stdin.readlines():
-        if line[:2] in prefixes:
-            print(line[2:], end=' ')
-
-if __name__ == '__main__':
-    import sys
-    args = sys.argv[1:]
-    if "-profile" in args:
-        import profile, pstats
-        args.remove("-profile")
-        statf = "ndiff.pro"
-        profile.run("main(args)", statf)
-        stats = pstats.Stats(statf)
-        stats.strip_dirs().sort_stats('time').print_stats()
-    else:
-        main(args)
diff --git a/src/zope/tal/runtest.py b/src/zope/tal/runtest.py
index 4bc35c9..3677902 100644
--- a/src/zope/tal/runtest.py
+++ b/src/zope/tal/runtest.py
@@ -21,6 +21,7 @@ import glob
 import os
 import sys
 import traceback
+import difflib
 
 from cStringIO import StringIO
 
@@ -31,22 +32,7 @@ import zope.tal.driver
 import zope.tal.tests.utils
 
 def showdiff(a, b):
-    from . import ndiff # XXX consider using difflib
-    cruncher = ndiff.SequenceMatcher(ndiff.IS_LINE_JUNK, a, b)
-    for tag, alo, ahi, blo, bhi in cruncher.get_opcodes():
-        if tag == "equal":
-            continue
-        print(nicerange(alo, ahi) + tag[0] + nicerange(blo, bhi))
-        ndiff.dump('<', a, alo, ahi)
-        if a and b:
-            print('---')
-        ndiff.dump('>', b, blo, bhi)
-
-def nicerange(lo, hi):
-    if hi <= lo+1:
-        return str(lo+1)
-    else:
-        return "%d,%d" % (lo+1, hi)
+    print(''.join(difflib.ndiff(a, b)))
 
 def main():
     opts = []