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authorStefan Israelsson Tampe <stefan.itampe@gmail.com>2018-11-06 23:26:25 +0100
committerStefan Israelsson Tampe <stefan.itampe@gmail.com>2018-11-06 23:26:25 +0100
commit4d4de6eecb3917e19a0af616790630a683b43767 (patch)
tree84f4e249a986928dfcba616d32a269900804772c /modules/language/python/module/#difflib.py#
parent9f1bcefabfbfb28cd913b363285675d98e9c622c (diff)
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+module(difflib)
+
+"""
+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', 'diff_bytes', 'HtmlDiff', 'Match']
+
+from heapq import nlargest as _nlargest
+from collections import namedtuple as _namedtuple
+
+Match = _namedtuple('Match', 'a b size')
+
+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='', autojunk=True):
+ """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().
+
+ Optional arg autojunk should be set to False to disable the
+ "automatic junk heuristic" that treats popular elements as junk
+ (see module documentation for more information).
+ """
+
+ # 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 and popular 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 "in self.bjunk".
+ # bjunk
+ # the items in b for which isjunk is True.
+ # bpopular
+ # nonjunk items in b treated as junk by the heuristic (if used).
+
+