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# Simple Diff for Python v 0.1
# (C) Paul Butler 2008 <>
# May be used and distributed under the zlib/libpng license
# <>
def diff(old, new):
"""Find the differences between two lists. Returns a list of pairs, where the first value
is in ['+','-','='] and represents an insertion, deletion, or no change for that list.
The second value of the pair is the list of elements."""
ohash = {}
for i, val in enumerate(old): # Build a hash map with elements from old as keys, and
# a list of indexes as values
# Find the largest substring common to old and new
lastRow = [0] * len(old)
subStartOld = subStartNew = subLength = 0
for j, val in enumerate(new):
thisRow = [0] * len(old)
for k in ohash.setdefault(val,[]):
thisRow[k] = (k and lastRow[k - 1]) + 1
if(thisRow[k] > subLength):
subLength = thisRow[k]
subStartOld = k - subLength + 1
subStartNew = j - subLength + 1
lastRow = thisRow
if subLength == 0: # If no common substring is found, assume that an insert and
# delete has taken place...
return (old and [('-', old)] or []) + (new and [('+', new)] or [])
else: # ...otherwise, the common substring is considered to have no change, and we recurse
# on the text before and after the substring
return diff(old[:subStartOld], new[:subStartNew]) + \
[('=', new[subStartNew:subStartNew + subLength])] + \
diff(old[subStartOld + subLength:], new[subStartNew + subLength:])
# The below functions are intended for simple tests and experimentation; you will want to write more sophisticated wrapper functions for real use
def stringDiff(old, new):
"""Returns the difference between the old and new strings when split on whitespace. Considers punctuation a part of the word"""
return diff(old.split(), new.split())
def htmlDiff(old, new):
"""Returns the difference between two strings (as in stringDiff) in HTML format."""
con = {'=': (lambda x: x),
'+': (lambda x: "<ins>" + x + "</ins>"),
'-': (lambda x: "<del>" + x + "</del>")}
return " ".join([(con[a])(" ".join(b)) for a, b in stringDiff(old, new)])
#print htmlDiff("The world is a tragedy to those who feel, but a comedy to those who think",
# "Life is a tragedy for those who feel, and a comedy to those who think") # Horace Walpole
#print htmlDiff("I have often regretted my speech, never my silence",
# "I have regretted my speech often, my silence never") # Xenocrates