199 lines
7.3 KiB
Python
199 lines
7.3 KiB
Python
'''
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Simple Diff for Python version 1.0
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Annotate two versions of a list with the values that have been
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changed between the versions, similar to unix's `diff` but with
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a dead-simple Python interface.
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(C) Paul Butler 2008-2012 <http://www.paulbutler.org/>
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May be used and distributed under the zlib/libpng license
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<http://www.opensource.org/licenses/zlib-license.php>
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'''
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__all__ = ['diff', 'string_diff', 'html_diff']
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__version__ = '1.0'
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def diff(old, new):
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'''
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Find the differences between two lists. Returns a list of pairs, where the
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first value is in ['+','-','='] and represents an insertion, deletion, or
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no change for that list. The second value of the pair is the list
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of elements.
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Params:
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old the old list of immutable, comparable values (ie. a list
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of strings)
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new the new list of immutable, comparable values
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Returns:
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A list of pairs, with the first part of the pair being one of three
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strings ('-', '+', '=') and the second part being a list of values from
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the original old and/or new lists. The first part of the pair
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corresponds to whether the list of values is a deletion, insertion, or
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unchanged, respectively.
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Examples:
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>>> diff([1,2,3,4],[1,3,4])
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[('=', [1]), ('-', [2]), ('=', [3, 4])]
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>>> diff([1,2,3,4],[2,3,4,1])
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[('-', [1]), ('=', [2, 3, 4]), ('+', [1])]
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>>> diff('The quick brown fox jumps over the lazy dog'.split(),
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... 'The slow blue cheese drips over the lazy carrot'.split())
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... # doctest: +NORMALIZE_WHITESPACE
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[('=', ['The']),
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('-', ['quick', 'brown', 'fox', 'jumps']),
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('+', ['slow', 'blue', 'cheese', 'drips']),
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('=', ['over', 'the', 'lazy']),
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('-', ['dog']),
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('+', ['carrot'])]
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'''
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# Create a map from old values to their indices
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old_index_map = dict()
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for i, val in enumerate(old):
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old_index_map.setdefault(val,list()).append(i)
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# Find the largest substring common to old and new.
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# We use a dynamic programming approach here.
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#
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# We iterate over each value in the `new` list, calling the
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# index `inew`. At each iteration, `overlap[i]` is the
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# length of the largest suffix of `old[:i]` equal to a suffix
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# of `new[:inew]` (or unset when `old[i]` != `new[inew]`).
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#
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# At each stage of iteration, the new `overlap` (called
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# `_overlap` until the original `overlap` is no longer needed)
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# is built from the old one.
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#
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# If the length of overlap exceeds the largest substring
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# seen so far (`sub_length`), we update the largest substring
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# to the overlapping strings.
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overlap = dict()
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# `sub_start_old` is the index of the beginning of the largest overlapping
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# substring in the old list. `sub_start_new` is the index of the beginning
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# of the same substring in the new list. `sub_length` is the length that
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# overlaps in both.
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# These track the largest overlapping substring seen so far, so naturally
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# we start with a 0-length substring.
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sub_start_old = 0
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sub_start_new = 0
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sub_length = 0
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for inew, val in enumerate(new):
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_overlap = dict()
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for iold in old_index_map.get(val,list()):
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# now we are considering all values of iold such that
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# `old[iold] == new[inew]`.
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_overlap[iold] = (iold and overlap.get(iold - 1, 0)) + 1
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if(_overlap[iold] > sub_length):
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# this is the largest substring seen so far, so store its
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# indices
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sub_length = _overlap[iold]
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sub_start_old = iold - sub_length + 1
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sub_start_new = inew - sub_length + 1
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overlap = _overlap
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if sub_length == 0:
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# If no common substring is found, we return an insert and delete...
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return (old and [('-', old)] or []) + (new and [('+', new)] or [])
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else:
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# ...otherwise, the common substring is unchanged and we recursively
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# diff the text before and after that substring
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return diff(old[ : sub_start_old], new[ : sub_start_new]) + \
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[('=', new[sub_start_new : sub_start_new + sub_length])] + \
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diff(old[sub_start_old + sub_length : ],
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new[sub_start_new + sub_length : ])
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def string_diff(old, new):
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'''
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Returns the difference between the old and new strings when split on
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whitespace. Considers punctuation a part of the word
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This function is intended as an example; you'll probably want
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a more sophisticated wrapper in practice.
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Params:
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old the old string
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new the new string
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Returns:
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the output of `diff` on the two strings after splitting them
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on whitespace (a list of change instructions; see the docstring
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of `diff`)
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Examples:
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>>> string_diff('The quick brown fox', 'The fast blue fox')
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... # doctest: +NORMALIZE_WHITESPACE
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[('=', ['The']),
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('-', ['quick', 'brown']),
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('+', ['fast', 'blue']),
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('=', ['fox'])]
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'''
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return diff(old.split(), new.split())
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def html_diff(old, new):
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'''
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Returns the difference between two strings (as in stringDiff) in
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HTML format. HTML code in the strings is NOT escaped, so you
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will get weird results if the strings contain HTML.
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This function is intended as an example; you'll probably want
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a more sophisticated wrapper in practice.
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Params:
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old the old string
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new the new string
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Returns:
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the output of the diff expressed with HTML <ins> and <del>
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tags.
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Examples:
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>>> html_diff('The quick brown fox', 'The fast blue fox')
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'The <del>quick brown</del> <ins>fast blue</ins> fox'
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'''
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con = {'=': (lambda x: x),
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'+': (lambda x: "<ins>" + x + "</ins>"),
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'-': (lambda x: "<del>" + x + "</del>")}
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return " ".join([(con[a])(" ".join(b)) for a, b in string_diff(old, new)])
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def check_diff(old, new):
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'''
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This tests that diffs returned by `diff` are valid. You probably won't
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want to use this function, but it's provided for documentation and
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testing.
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A diff should satisfy the property that the old input is equal to the
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elements of the result annotated with '-' or '=' concatenated together.
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Likewise, the new input is equal to the elements of the result annotated
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with '+' or '=' concatenated together. This function compares `old`,
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`new`, and the results of `diff(old, new)` to ensure this is true.
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Tests:
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>>> check_diff('ABCBA', 'CBABA')
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>>> check_diff('Foobarbaz', 'Foobarbaz')
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>>> check_diff('Foobarbaz', 'Boobazbam')
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>>> check_diff('The quick brown fox', 'Some quick brown car')
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>>> check_diff('A thick red book', 'A quick blue book')
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>>> check_diff('dafhjkdashfkhasfjsdafdasfsda', 'asdfaskjfhksahkfjsdha')
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>>> check_diff('88288822828828288282828', '88288882882828282882828')
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>>> check_diff('1234567890', '24689')
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'''
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old = list(old)
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new = list(new)
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result = diff(old, new)
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_old = [val for (a, vals) in result if (a in '=-') for val in vals]
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assert old == _old, 'Expected %s, got %s' % (old, _old)
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_new = [val for (a, vals) in result if (a in '=+') for val in vals]
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assert new == _new, 'Expected %s, got %s' % (new, _new)
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