Issue #24109: Include Tools/scripts/diff.py instead of duplicating it in difflib documentation.

Patch by Keith Gray.

Doc/library/difflib.rst

@@ -743,65 +743,4 @@ This example shows how to use difflib to create a ``diff``-like utility.
 It is also contained in the Python source distribution, as
 :file:`Tools/scripts/diff.py`.
 
-.. testcode::
+.. literalinclude:: ../../Tools/scripts/diff.py
-
-   """ Command line interface to difflib.py providing diffs in four formats:
-
-   * ndiff:    lists every line and highlights interline changes.
-   * context:  highlights clusters of changes in a before/after format.
-   * unified:  highlights clusters of changes in an inline format.
-   * html:     generates side by side comparison with change highlights.
-
-   """
-
-   import sys, os, time, difflib, optparse
-
-   def main():
-        # Configure the option parser
-       usage = "usage: %prog [options] fromfile tofile"
-       parser = optparse.OptionParser(usage)
-       parser.add_option("-c", action="store_true", default=False,
-                         help='Produce a context format diff (default)')
-       parser.add_option("-u", action="store_true", default=False,
-                         help='Produce a unified format diff')
-       hlp = 'Produce HTML side by side diff (can use -c and -l in conjunction)'
-       parser.add_option("-m", action="store_true", default=False, help=hlp)
-       parser.add_option("-n", action="store_true", default=False,
-                         help='Produce a ndiff format diff')
-       parser.add_option("-l", "--lines", type="int", default=3,
-                         help='Set number of context lines (default 3)')
-       (options, args) = parser.parse_args()
-
-       if len(args) == 0:
-           parser.print_help()
-           sys.exit(1)
-       if len(args) != 2:
-           parser.error("need to specify both a fromfile and tofile")
-
-       n = options.lines
-       fromfile, tofile = args # as specified in the usage string
-
-       # we're passing these as arguments to the diff function
-       fromdate = time.ctime(os.stat(fromfile).st_mtime)
-       todate = time.ctime(os.stat(tofile).st_mtime)
-       with open(fromfile) as fromf, open(tofile) as tof:
-           fromlines, tolines = list(fromf), list(tof)
-
-       if options.u:
-           diff = difflib.unified_diff(fromlines, tolines, fromfile, tofile,
-                                       fromdate, todate, n=n)
-       elif options.n:
-           diff = difflib.ndiff(fromlines, tolines)
-       elif options.m:
-           diff = difflib.HtmlDiff().make_file(fromlines, tolines, fromfile,
-                                               tofile, context=options.c,
-                                               numlines=n)
-       else:
-           diff = difflib.context_diff(fromlines, tolines, fromfile, tofile,
-                                       fromdate, todate, n=n)
-
-       # we're using writelines because diff is a generator
-       sys.stdout.writelines(diff)
-
-   if __name__ == '__main__':
-       main()