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diff-match-patch/python3/diff_match_patch.py at patch-1 · atdrendel/diff-match-patch · GitHub
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#!/usr/bin/python3
"""Diff Match and Patch
Copyright 2018 The diff-match-patch Authors.
https://github.com/google/diff-match-patch
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""
"""Functions for diff, match and patch.
Computes the difference between two texts to create a patch.
Applies the patch onto another text, allowing for errors.
"""
__author__
=
'fraser@google.com (Neil Fraser)'
import
re
import
sys
import
time
import
urllib
.
parse
class
diff_match_patch
:
"""Class containing the diff, match and patch methods.
Also contains the behaviour settings.
"""
def
__init__
(
self
):
"""Inits a diff_match_patch object with default settings.
Redefine these in your program to override the defaults.
"""
# Number of seconds to map a diff before giving up (0 for infinity).
self
.
Diff_Timeout
=
1.0
# Cost of an empty edit operation in terms of edit characters.
self
.
Diff_EditCost
=
4
# At what point is no match declared (0.0 = perfection, 1.0 = very loose).
self
.
Match_Threshold
=
0.5
# How far to search for a match (0 = exact location, 1000+ = broad match).
# A match this many characters away from the expected location will add
# 1.0 to the score (0.0 is a perfect match).
self
.
Match_Distance
=
1000
# When deleting a large block of text (over ~64 characters), how close do
# the contents have to be to match the expected contents. (0.0 = perfection,
# 1.0 = very loose). Note that Match_Threshold controls how closely the
# end points of a delete need to match.
self
.
Patch_DeleteThreshold
=
0.5
# Chunk size for context length.
self
.
Patch_Margin
=
4
# The number of bits in an int.
# Python has no maximum, thus to disable patch splitting set to 0.
# However to avoid long patches in certain pathological cases, use 32.
# Multiple short patches (using native ints) are much faster than long ones.
self
.
Match_MaxBits
=
32
# DIFF FUNCTIONS
# The data structure representing a diff is an array of tuples:
# [(DIFF_DELETE, "Hello"), (DIFF_INSERT, "Goodbye"), (DIFF_EQUAL, " world.")]
# which means: delete "Hello", add "Goodbye" and keep " world."
DIFF_DELETE
=
-
1
DIFF_INSERT
=
1
DIFF_EQUAL
=
0
def
diff_main
(
self
,
text1
,
text2
,
checklines
=
True
,
deadline
=
None
):
"""Find the differences between two texts. Simplifies the problem by
stripping any common prefix or suffix off the texts before diffing.
Args:
text1: Old string to be diffed.
text2: New string to be diffed.
checklines: Optional speedup flag. If present and false, then don't run
a line-level diff first to identify the changed areas.
Defaults to true, which does a faster, slightly less optimal diff.
deadline: Optional time when the diff should be complete by. Used
internally for recursive calls. Users should set DiffTimeout instead.
Returns:
Array of changes.
"""
# Set a deadline by which time the diff must be complete.
if
deadline
==
None
:
# Unlike in most languages, Python counts time in seconds.
if
self
.
Diff_Timeout
<=
0
:
deadline
=
sys
.
maxsize
else
:
deadline
=
time
.
time
()
+
self
.
Diff_Timeout
# Check for null inputs.
if
text1
==
None
or
text2
==
None
:
raise
ValueError
(
"Null inputs. (diff_main)"
)
# Check for equality (speedup).
if
text1
==
text2
:
if
text1
:
return
[(
self
.
DIFF_EQUAL
,
text1
)]
return
[]
# Trim off common prefix (speedup).
commonlength
=
self
.
diff_commonPrefix
(
text1
,
text2
)
commonprefix
=
text1
[:
commonlength
]
text1
=
text1
[
commonlength
:]
text2
=
text2
[
commonlength
:]
# Trim off common suffix (speedup).
commonlength
=
self
.
diff_commonSuffix
(
text1
,
text2
)
if
commonlength
==
0
:
commonsuffix
=
''
else
:
commonsuffix
=
text1
[
-
commonlength
:]
text1
=
text1
[:
-
commonlength
]
text2
=
text2
[:
-
commonlength
]
# Compute the diff on the middle block.
diffs
=
self
.
diff_compute
(
text1
,
text2
,
checklines
,
deadline
)
# Restore the prefix and suffix.
if
commonprefix
:
diffs
[:
0
]
=
[(
self
.
DIFF_EQUAL
,
commonprefix
)]
if
commonsuffix
:
diffs
.
append
((
self
.
DIFF_EQUAL
,
commonsuffix
))
self
.
diff_cleanupMerge
(
diffs
)
return
diffs
def
diff_compute
(
self
,
text1
,
text2
,
checklines
,
deadline
):
"""Find the differences between two texts. Assumes that the texts do not
have any common prefix or suffix.
Args:
text1: Old string to be diffed.
text2: New string to be diffed.
checklines: Speedup flag. If false, then don't run a line-level diff
first to identify the changed areas.
If true, then run a faster, slightly less optimal diff.
deadline: Time when the diff should be complete by.
Returns:
Array of changes.
"""
if
not
text1
:
# Just add some text (speedup).
return
[(
self
.
DIFF_INSERT
,
text2
)]
if
not
text2
:
# Just delete some text (speedup).
return
[(
self
.
DIFF_DELETE
,
text1
)]
if
len
(
text1
)
>
len
(
text2
):
(
longtext
,
shorttext
)
=
(
text1
,
text2
)
else
:
(
shorttext
,
longtext
)
=
(
text1
,
text2
)
i
=
longtext
.
find
(
shorttext
)
if
i
!=
-
1
:
# Shorter text is inside the longer text (speedup).
diffs
=
[(
self
.
DIFF_INSERT
,
longtext
[:
i
]), (
self
.
DIFF_EQUAL
,
shorttext
),
(
self
.
DIFF_INSERT
,
longtext
[
i
+
len
(
shorttext
):])]
# Swap insertions for deletions if diff is reversed.
if
len
(
text1
)
>
len
(
text2
):
diffs
[
0
]
=
(
self
.
DIFF_DELETE
,
diffs
[
0
][
1
])
diffs
[
2
]
=
(
self
.
DIFF_DELETE
,
diffs
[
2
][
1
])
return
diffs
if
len
(
shorttext
)
==
1
:
# Single character string.
# After the previous speedup, the character can't be an equality.
return
[(
self
.
DIFF_DELETE
,
text1
), (
self
.
DIFF_INSERT
,
text2
)]
# Check to see if the problem can be split in two.
hm
=
self
.
diff_halfMatch
(
text1
,
text2
)
if
hm
:
# A half-match was found, sort out the return data.
(
text1_a
,
text1_b
,
text2_a
,
text2_b
,
mid_common
)
=
hm
# Send both pairs off for separate processing.
diffs_a
=
self
.
diff_main
(
text1_a
,
text2_a
,
checklines
,
deadline
)
diffs_b
=
self
.
diff_main
(
text1_b
,
text2_b
,
checklines
,
deadline
)
# Merge the results.
return
diffs_a
+
[(
self
.
DIFF_EQUAL
,
mid_common
)]
+
diffs_b
if
checklines
and
len
(
text1
)
>
100
and
len
(
text2
)
>
100
:
return
self
.
diff_lineMode
(
text1
,
text2
,
deadline
)
return
self
.
diff_bisect
(
text1
,
text2
,
deadline
)
def
diff_lineMode
(
self
,
text1
,
text2
,
deadline
):
"""Do a quick line-level diff on both strings, then rediff the parts for
greater accuracy.
This speedup can produce non-minimal diffs.
Args:
text1: Old string to be diffed.
text2: New string to be diffed.
deadline: Time when the diff should be complete by.
Returns:
Array of changes.
"""
# Scan the text on a line-by-line basis first.
(
text1
,
text2
,
linearray
)
=
self
.
diff_linesToChars
(
text1
,
text2
)
diffs
=
self
.
diff_main
(
text1
,
text2
,
False
,
deadline
)
# Convert the diff back to original text.
self
.
diff_charsToLines
(
diffs
,
linearray
)
# Eliminate freak matches (e.g. blank lines)
self
.
diff_cleanupSemantic
(
diffs
)
# Rediff any replacement blocks, this time character-by-character.
# Add a dummy entry at the end.
diffs
.
append
((
self
.
DIFF_EQUAL
,
''
))
pointer
=
0
count_delete
=
0
count_insert
=
0
text_delete
=
''
text_insert
=
''
while
pointer
<
len
(
diffs
):
if
diffs
[
pointer
][
0
]
==
self
.
DIFF_INSERT
:
count_insert
+=
1
text_insert
+=
diffs
[
pointer
][
1
]
elif
diffs
[
pointer
][
0
]
==
self
.
DIFF_DELETE
:
count_delete
+=
1
text_delete
+=
diffs
[
pointer
][
1
]
elif
diffs
[
pointer
][
0
]
==
self
.
DIFF_EQUAL
:
# Upon reaching an equality, check for prior redundancies.
if
count_delete
>=
1
and
count_insert
>=
1
:
# Delete the offending records and add the merged ones.
subDiff
=
self
.
diff_main
(
text_delete
,
text_insert
,
False
,
deadline
)
diffs
[
pointer
-
count_delete
-
count_insert
:
pointer
]
=
subDiff
pointer
=
pointer
-
count_delete
-
count_insert
+
len
(
subDiff
)
count_insert
=
0
count_delete
=
0
text_delete
=
''
text_insert
=
''
pointer
+=
1
diffs
.
pop
()
# Remove the dummy entry at the end.
return
diffs
def
diff_bisect
(
self
,
text1
,
text2
,
deadline
):
"""Find the 'middle snake' of a diff, split the problem in two
and return the recursively constructed diff.
See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
Args:
text1: Old string to be diffed.
text2: New string to be diffed.
deadline: Time at which to bail if not yet complete.
Returns:
Array of diff tuples.
"""
# Cache the text lengths to prevent multiple calls.
text1_length
=
len
(
text1
)
text2_length
=
len
(
text2
)
max_d
=
(
text1_length
+
text2_length
+
1
)
//
2
v_offset
=
max_d
v_length
=
2
*
max_d
v1
=
[
-
1
]
*
v_length
v1
[
v_offset
+
1
]
=
0
v2
=
v1
[:]
delta
=
text1_length
-
text2_length
# If the total number of characters is odd, then the front path will
# collide with the reverse path.
front
=
(
delta
%
2
!=
0
)
# Offsets for start and end of k loop.
# Prevents mapping of space beyond the grid.
k1start
=
0
k1end
=
0
k2start
=
0
k2end
=
0
for
d
in
range
(
max_d
):
# Bail out if deadline is reached.
if
time
.
time
()
>
deadline
:
break
# Walk the front path one step.
for
k1
in
range
(
-
d
+
k1start
,
d
+
1
-
k1end
,
2
):
k1_offset
=
v_offset
+
k1
if
k1
==
-
d
or
(
k1
!=
d
and
v1
[
k1_offset
-
1
]
<
v1
[
k1_offset
+
1
]):
x1
=
v1
[
k1_offset
+
1
]
else
:
x1
=
v1
[
k1_offset
-
1
]
+
1
y1
=
x1
-
k1
while
(
x1
<
text1_length
and
y1
<
text2_length
and
text1
[
x1
]
==
text2
[
y1
]):
x1
+=
1
y1
+=
1
v1
[
k1_offset
]
=
x1
if
x1
>
text1_length
:
# Ran off the right of the graph.
k1end
+=
2
elif
y1
>
text2_length
:
# Ran off the bottom of the graph.
k1start
+=
2
elif
front
:
k2_offset
=
v_offset
+
delta
-
k1
if
k2_offset
>=
0
and
k2_offset
<
v_length
and
v2
[
k2_offset
]
!=
-
1
:
# Mirror x2 onto top-left coordinate system.
x2
=
text1_length
-
v2
[
k2_offset
]
if
x1
>=
x2
:
# Overlap detected.
return
self
.
diff_bisectSplit
(
text1
,
text2
,
x1
,
y1
,
deadline
)
# Walk the reverse path one step.
for
k2
in
range
(
-
d
+
k2start
,
d
+
1
-
k2end
,
2
):
k2_offset
=
v_offset
+
k2
if
k2
==
-
d
or
(
k2
!=
d
and
v2
[
k2_offset
-
1
]
<
v2
[
k2_offset
+
1
]):
x2
=
v2
[
k2_offset
+
1
]
else
:
x2
=
v2
[
k2_offset
-
1
]
+
1
y2
=
x2
-
k2
while
(
x2
<
text1_length
and
y2
<
text2_length
and
text1
[
-
x2
-
1
]
==
text2
[
-
y2
-
1
]):
x2
+=
1
y2
+=
1
v2
[
k2_offset
]
=
x2
if
x2
>
text1_length
:
# Ran off the left of the graph.
k2end
+=
2
elif
y2
>
text2_length
:
# Ran off the top of the graph.
k2start
+=
2
elif
not
front
:
k1_offset
=
v_offset
+
delta
-
k2
if
k1_offset
>=
0
and
k1_offset
<
v_length
and
v1
[
k1_offset
]
!=
-
1
:
x1
=
v1
[
k1_offset
]
y1
=
v_offset
+
x1
-
k1_offset
# Mirror x2 onto top-left coordinate system.
x2
=
text1_length
-
x2
if
x1
>=
x2
:
# Overlap detected.
return
self
.
diff_bisectSplit
(
text1
,
text2
,
x1
,
y1
,
deadline
)
# Diff took too long and hit the deadline or
# number of diffs equals number of characters, no commonality at all.
return
[(
self
.
DIFF_DELETE
,
text1
), (
self
.
DIFF_INSERT
,
text2
)]
def
diff_bisectSplit
(
self
,
text1
,
text2
,
x
,
y
,
deadline
):
"""Given the location of the 'middle snake', split the diff in two parts
and recurse.
Args:
text1: Old string to be diffed.
text2: New string to be diffed.
x: Index of split point in text1.
y: Index of split point in text2.
deadline: Time at which to bail if not yet complete.
Returns:
Array of diff tuples.
"""
text1a
=
text1
[:
x
]
text2a
=
text2
[:
y
]
text1b
=
text1
[
x
:]
text2b
=
text2
[
y
:]
# Compute both diffs serially.
diffs
=
self
.
diff_main
(
text1a
,
text2a
,
False
,
deadline
)
diffsb
=
self
.
diff_main
(
text1b
,
text2b
,
False
,
deadline
)
return
diffs
+
diffsb
def
diff_linesToChars
(
self
,
text1
,
text2
):
"""Split two texts into an array of strings. Reduce the texts to a string
of hashes where each Unicode character represents one line.
Args:
text1: First string.
text2: Second string.
Returns:
Three element tuple, containing the encoded text1, the encoded text2 and
the array of unique strings. The zeroth element of the array of unique
strings is intentionally blank.
"""
lineArray
=
[]
# e.g. lineArray[4] == "Hello\n"
lineHash
=
{}
# e.g. lineHash["Hello\n"] == 4
# "\x00" is a valid character, but various debuggers don't like it.
# So we'll insert a junk entry to avoid generating a null character.
lineArray
.
append
(
''
)
def
diff_linesToCharsMunge
(
text
):
"""Split a text into an array of strings. Reduce the texts to a string
of hashes where each Unicode character represents one line.
Modifies linearray and linehash through being a closure.
Args:
text: String to encode.
Returns:
Encoded string.
"""
chars
=
[]
# Walk the text, pulling out a substring for each line.
# text.split('\n') would would temporarily double our memory footprint.
# Modifying text would create many large strings to garbage collect.
lineStart
=
0
lineEnd
=
-
1
while
lineEnd
<
len
(
text
)
-
1
:
lineEnd
=
text
.
find
(
'
\n
'
,
lineStart
)
if
lineEnd
==
-
1
:
lineEnd
=
len
(
text
)
-
1
line
=
text
[
lineStart
:
lineEnd
+
1
]
if
line
in
lineHash
:
chars
.
append
(
chr
(
lineHash
[
line
]))
else
:
if
len
(
lineArray
)
==
maxLines
:
# Bail out at 1114111 because chr(1114112) throws.
line
=
text
[
lineStart
:]
lineEnd
=
len
(
text
)
lineArray
.
append
(
line
)
lineHash
[
line
]
=
len
(
lineArray
)
-
1
chars
.
append
(
chr
(
len
(
lineArray
)
-
1
))
lineStart
=
lineEnd
+
1
return
""
.
join
(
chars
)
# Allocate 2/3rds of the space for text1, the rest for text2.
maxLines
=
666666
chars1
=
diff_linesToCharsMunge
(
text1
)
maxLines
=
1114111
chars2
=
diff_linesToCharsMunge
(
text2
)
return
(
chars1
,
chars2
,
lineArray
)
def
diff_charsToLines
(
self
,
diffs
,
lineArray
):
"""Rehydrate the text in a diff from a string of line hashes to real lines
of text.
Args:
diffs: Array of diff tuples.
lineArray: Array of unique strings.
"""
for
i
in
range
(
len
(
diffs
)):
text
=
[]
for
char
in
diffs
[
i
][
1
]:
text
.
append
(
lineArray
[
ord
(
char
)])
diffs
[
i
]
=
(
diffs
[
i
][
0
],
""
.
join
(
text
))
def
diff_commonPrefix
(
self
,
text1
,
text2
):
"""Determine the common prefix of two strings.
Args:
text1: First string.
text2: Second string.
Returns:
The number of characters common to the start of each string.
"""
# Quick check for common null cases.
if
not
text1
or
not
text2
or
text1
[
0
]
!=
text2
[
0
]:
return
0
# Binary search.
# Performance analysis: https://neil.fraser.name/news/2007/10/09/
pointermin
=
0
pointermax
=
min
(
len
(
text1
),
len
(
text2
))
pointermid
=
pointermax
pointerstart
=
0
while
pointermin
<
pointermid
:
if
text1
[
pointerstart
:
pointermid
]
==
text2
[
pointerstart
:
pointermid
]:
pointermin
=
pointermid
pointerstart
=
pointermin
else
:
pointermax
=
pointermid
pointermid
=
(
pointermax
-
pointermin
)
//
2
+
pointermin
return
pointermid
def
diff_commonSuffix
(
self
,
text1
,
text2
):
"""Determine the common suffix of two strings.
Args:
text1: First string.
text2: Second string.
Returns:
The number of characters common to the end of each string.
"""
# Quick check for common null cases.
if
not
text1
or
not
text2
or
text1
[
-
1
]
!=
text2
[
-
1
]:
return
0
# Binary search.
# Performance analysis: https://neil.fraser.name/news/2007/10/09/
pointermin
=
0
pointermax
=
min
(
len
(
text1
),
len
(
text2
))
pointermid
=
pointermax
pointerend
=
0
while
pointermin
<
pointermid
:
if
(
text1
[
-
pointermid
:
len
(
text1
)
-
pointerend
]
==
text2
[
-
pointermid
:
len
(
text2
)
-
pointerend
]):
pointermin
=
pointermid
pointerend
=
pointermin
else
:
pointermax
=
pointermid
pointermid
=
(
pointermax
-
pointermin
)
//
2
+
pointermin
return
pointermid
def
diff_commonOverlap
(
self
,
text1
,
text2
):
"""Determine if the suffix of one string is the prefix of another.
Args:
text1 First string.
text2 Second string.
Returns:
The number of characters common to the end of the first
string and the start of the second string.
"""
# Cache the text lengths to prevent multiple calls.
text1_length
=
len
(
text1
)
text2_length
=
len
(
text2
)
# Eliminate the null case.
if
text1_length
==
0
or
text2_length
==
0
:
return
0
# Truncate the longer string.
if
text1_length
>
text2_length
:
text1
=
text1
[
-
text2_length
:]
elif
text1_length
<
text2_length
:
text2
=
text2
[:
text1_length
]
text_length
=
min
(
text1_length
,
text2_length
)
# Quick check for the worst case.
if
text1
==
text2
:
return
text_length
# Start by looking for a single character match
# and increase length until no match is found.
# Performance analysis: https://neil.fraser.name/news/2010/11/04/
best
=
0
length
=
1
while
True
:
pattern
=
text1
[
-
length
:]
found
=
text2
.
find
(
pattern
)
if
found
==
-
1
:
return
best
length
+=
found
if
found
==
0
or
text1
[
-
length
:]
==
text2
[:
length
]:
best
=
length
length
+=
1
def
diff_halfMatch
(
self
,
text1
,
text2
):
"""Do the two texts share a substring which is at least half the length of
the longer text?
This speedup can produce non-minimal diffs.
Args:
text1: First string.
text2: Second string.
Returns:
Five element Array, containing the prefix of text1, the suffix of text1,
the prefix of text2, the suffix of text2 and the common middle. Or None
if there was no match.
"""
if
self
.
Diff_Timeout
<=
0
:
# Don't risk returning a non-optimal diff if we have unlimited time.
return
None
if
len
(
text1
)
>
len
(
text2
):
(
longtext
,
shorttext
)
=
(
text1
,
text2
)
else
:
(
shorttext
,
longtext
)
=
(
text1
,
text2
)
if
len
(
longtext
)
<
4
or
len
(
shorttext
)
*
2
<
len
(
longtext
):
return
None
# Pointless.
def
diff_halfMatchI
(
longtext
,
shorttext
,
i
):
"""Does a substring of shorttext exist within longtext such that the
substring is at least half the length of longtext?
Closure, but does not reference any external variables.
Args:
longtext: Longer string.
shorttext: Shorter string.
i: Start index of quarter length substring within longtext.
Returns:
Five element Array, containing the prefix of longtext, the suffix of
longtext, the prefix of shorttext, the suffix of shorttext and the
common middle. Or None if there was no match.
"""
seed
=
longtext
[
i
:
i
+
len
(
longtext
)
//
4
]
best_common
=
''
j
=
shorttext
.
find
(
seed
)
while
j
!=
-
1
:
prefixLength
=
self
.
diff_commonPrefix
(
longtext
[
i
:],
shorttext
[
j
:])
suffixLength
=
self
.
diff_commonSuffix
(
longtext
[:
i
],
shorttext
[:
j
])
if
len
(
best_common
)
<
suffixLength
+
prefixLength
:
best_common
=
(
shorttext
[
j
-
suffixLength
:
j
]
+
shorttext
[
j
:
j
+
prefixLength
])
best_longtext_a
=
longtext
[:
i
-
suffixLength
]
best_longtext_b
=
longtext
[
i
+
prefixLength
:]
best_shorttext_a
=
shorttext
[:
j
-
suffixLength
]
best_shorttext_b
=
shorttext
[
j
+
prefixLength
:]
j
=
shorttext
.
find
(
seed
,
j
+
1
)
if
len
(
best_common
)
*
2
>=
len
(
longtext
):
return
(
best_longtext_a
,
best_longtext_b
,
best_shorttext_a
,
best_shorttext_b
,
best_common
)
else
:
return
None
# First check if the second quarter is the seed for a half-match.
hm1
=
diff_halfMatchI
(
longtext
,
shorttext
, (
len
(
longtext
)
+
3
)
//
4
)
# Check again based on the third quarter.
hm2
=
diff_halfMatchI
(
longtext
,
shorttext
, (
len
(
longtext
)
+
1
)
//
2
)
if
not
hm1
and
not
hm2
:
return
None
elif
not
hm2
:
hm
=
hm1
elif
not
hm1
:
hm
=
hm2
else
:
# Both matched. Select the longest.
if
len
(
hm1
[
4
])
>
len
(
hm2
[
4
]):
hm
=
hm1
else
:
hm
=
hm2
# A half-match was found, sort out the return data.
if
len
(
text1
)
>
len
(
text2
):
(
text1_a
,
text1_b
,
text2_a
,
text2_b
,
mid_common
)
=
hm
else
:
(
text2_a
,
text2_b
,
text1_a
,
text1_b
,
mid_common
)
=
hm
return
(
text1_a
,
text1_b
,
text2_a
,
text2_b
,
mid_common
)
def
diff_cleanupSemantic
(
self
,
diffs
):
"""Reduce the number of edits by eliminating semantically trivial
equalities.
Args:
diffs: Array of diff tuples.
"""
changes
=
False
equalities
=
[]
# Stack of indices where equalities are found.
lastEquality
=
None
# Always equal to diffs[equalities[-1]][1]
pointer
=
0
# Index of current position.
# Number of chars that changed prior to the equality.
length_insertions1
,
length_deletions1
=
0
,
0
# Number of chars that changed after the equality.
length_insertions2
,
length_deletions2
=
0
,
0
while
pointer
<
len
(
diffs
):
if
diffs
[
pointer
][
0
]
==
self
.
DIFF_EQUAL
:
# Equality found.
equalities
.
append
(
pointer
)
length_insertions1
,
length_insertions2
=
length_insertions2
,
0
length_deletions1
,
length_deletions2
=
length_deletions2
,
0
lastEquality
=
diffs
[
pointer
][
1
]
else
:
# An insertion or deletion.
if
diffs
[
pointer
][
0
]
==
self
.
DIFF_INSERT
:
length_insertions2
+=
len
(
diffs
[
pointer
][
1
])
else
:
length_deletions2
+=
len
(
diffs
[
pointer
][
1
])
# Eliminate an equality that is smaller or equal to the edits on both
# sides of it.
if
(
lastEquality
and
(
len
(
lastEquality
)
<=
max
(
length_insertions1
,
length_deletions1
))
and
(
len
(
lastEquality
)
<=
max
(
length_insertions2
,
length_deletions2
))):
# Duplicate record.
diffs
.
insert
(
equalities
[
-
1
], (
self
.
DIFF_DELETE
,
lastEquality
))
# Change second copy to insert.
diffs
[
equalities
[
-
1
]
+
1
]
=
(
self
.
DIFF_INSERT
,
diffs
[
equalities
[
-
1
]
+
1
][
1
])
# Throw away the equality we just deleted.
equalities
.
pop
()
# Throw away the previous equality (it needs to be reevaluated).
if
len
(
equalities
):
equalities
.
pop
()
if
len
(
equalities
):
pointer
=
equalities
[
-
1
]
else
:
pointer
=
-
1
# Reset the counters.
length_insertions1
,
length_deletions1
=
0
,
0
length_insertions2
,
length_deletions2
=
0
,
0
lastEquality
=
None
changes
=
True
pointer
+=
1
# Normalize the diff.
if
changes
:
self
.
diff_cleanupMerge
(
diffs
)
self
.
diff_cleanupSemanticLossless
(
diffs
)
# Find any overlaps between deletions and insertions.
# e.g: <del>abcxxx</del><ins>xxxdef</ins>
# -> <del>abc</del>xxx<ins>def</ins>
# e.g: <del>xxxabc</del><ins>defxxx</ins>
# -> <ins>def</ins>xxx<del>abc</del>
# Only extract an overlap if it is as big as the edit ahead or behind it.
pointer
=
1
while
pointer
<
len
(
diffs
):
if
(
diffs
[
pointer
-
1
][
0
]
==
self
.
DIFF_DELETE
and
diffs
[
pointer
][
0
]
==
self
.
DIFF_INSERT
):
deletion
=
diffs
[
pointer
-
1
][
1
]
insertion
=
diffs
[
pointer
][
1
]
overlap_length1
=
self
.
diff_commonOverlap
(
deletion
,
insertion
)
overlap_length2
=
self
.
diff_commonOverlap
(
insertion
,
deletion
)
if
overlap_length1
>=
overlap_length2
:
if
(
overlap_length1
>=
len
(
deletion
)
/
2.0
or
overlap_length1
>=
len
(
insertion
)
/
2.0
):
# Overlap found. Insert an equality and trim the surrounding edits.
diffs
.
insert
(
pointer
, (
self
.
DIFF_EQUAL
,
insertion
[:
overlap_length1
]))
diffs
[
pointer
-
1
]
=
(
self
.
DIFF_DELETE
,
deletion
[:
len
(
deletion
)
-
overlap_length1
])
diffs
[
pointer
+
1
]
=
(
self
.
DIFF_INSERT
,
insertion
[
overlap_length1
:])
pointer
+=
1
else
:
if
(
overlap_length2
>=
len
(
deletion
)
/
2.0
or
overlap_length2
>=
len
(
insertion
)
/
2.0
):
# Reverse overlap found.
# Insert an equality and swap and trim the surrounding edits.
diffs
.
insert
(
pointer
, (
self
.
DIFF_EQUAL
,
deletion
[:
overlap_length2
]))
diffs
[
pointer
-
1
]
=
(
self
.
DIFF_INSERT
,
insertion
[:
len
(
insertion
)
-
overlap_length2
])
diffs
[
pointer
+
1
]
=
(
self
.
DIFF_DELETE
,
deletion
[
overlap_length2
:])
pointer
+=
1
pointer
+=
1
pointer
+=
1
def
diff_cleanupSemanticLossless
(
self
,
diffs
):
"""Look for single edits surrounded on both sides by equalities
which can be shifted sideways to align the edit to a word boundary.
e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
Args:
diffs: Array of diff tuples.
"""
def
diff_cleanupSemanticScore
(
one
,
two
):
"""Given two strings, compute a score representing whether the
internal boundary falls on logical boundaries.
Scores range from 6 (best) to 0 (worst).
Closure, but does not reference any external variables.
Args:
one: First string.
two: Second string.
Returns:
The score.
"""
if
not
one
or
not
two
:
# Edges are the best.
return
6
# Each port of this function behaves slightly differently due to
# subtle differences in each language's definition of things like
# 'whitespace'. Since this function's purpose is largely cosmetic,
# the choice has been made to use each language's native features
# rather than force total conformity.
char1
=
one
[
-
1
]
char2
=
two
[
0
]
nonAlphaNumeric1
=
not
char1
.
isalnum
()
nonAlphaNumeric2
=
not
char2
.
isalnum
()
whitespace1
=
nonAlphaNumeric1
and
char1
.
isspace
()
whitespace2
=
nonAlphaNumeric2
and
char2
.
isspace
()
lineBreak1
=
whitespace1
and
(
char1
==
"
\r
"
or
char1
==
"
\n
"
)
lineBreak2
=
whitespace2
and
(
char2
==
"
\r
"
or
char2
==
"
\n
"
)
blankLine1
=
lineBreak1
and
self
.
BLANKLINEEND
.
search
(
one
)
blankLine2
=
lineBreak2
and
self
.
BLANKLINESTART
.
match
(
two
)
if
blankLine1
or
blankLine2
:
# Five points for blank lines.
return
5
elif
lineBreak1
or
lineBreak2
:
# Four points for line breaks.
return
4
elif
nonAlphaNumeric1
and
not
whitespace1
and
whitespace2
:
# Three points for end of sentences.
return
3
elif
whitespace1
or
whitespace2
:
# Two points for whitespace.
return
2
elif
nonAlphaNumeric1
or
nonAlphaNumeric2
:
# One point for non-alphanumeric.
return
1
return
0
pointer
=
1
# Intentionally ignore the first and last element (don't need checking).
while
pointer
<
len
(
diffs
)
-
1
:
if
(
diffs
[
pointer
-
1
][
0
]
==
self
.
DIFF_EQUAL
and
diffs
[
pointer
+
1
][
0
]
==
self
.
DIFF_EQUAL
):
# This is a single edit surrounded by equalities.
equality1
=
diffs
[
pointer
-
1
][
1
]
edit
=
diffs
[
pointer
][
1
]
equality2
=
diffs
[
pointer
+
1
][
1
]
# First, shift the edit as far left as possible.
commonOffset
=
self
.
diff_commonSuffix
(
equality1
,
edit
)
if
commonOffset
:
commonString
=
edit
[
-
commonOffset
:]
equality1
=
equality1
[:
-
commonOffset
]
edit
=
commonString
+
edit
[:
-
commonOffset
]
equality2
=
commonString
+
equality2
# Second, step character by character right, looking for the best fit.
bestEquality1
=
equality1
bestEdit
=
edit
bestEquality2
=
equality2
bestScore
=
(
diff_cleanupSemanticScore
(
equality1
,
edit
)
+
diff_cleanupSemanticScore
(
edit
,
equality2
))
while
edit
and
equality2
and
edit
[
0
]
==
equality2
[
0
]:
equality1
+=
edit
[
0
]
edit
=
edit
[
1
:]
+
equality2
[
0
]
equality2
=
equality2
[
1
:]
score
=
(
diff_cleanupSemanticScore
(
equality1
,
edit
)
+
diff_cleanupSemanticScore
(
edit
,
equality2
))
# The >= encourages trailing rather than leading whitespace on edits.
if
score
>=
bestScore
:
bestScore
=
score
bestEquality1
=
equality1
bestEdit
=
edit
bestEquality2
=
equality2
if
diffs
[
pointer
-
1
][
1
]
!=
bestEquality1
:
# We have an improvement, save it back to the diff.
if
bestEquality1
:
diffs
[
pointer
-
1
]
=
(
diffs
[
pointer
-
1
][
0
],
bestEquality1
)
else
:
del
diffs
[
pointer
-
1
]
pointer
-=
1
diffs
[
pointer
]
=
(
diffs
[
pointer
][
0
],
bestEdit
)
if
bestEquality2
:
diffs
[
pointer
+
1
]
=
(
diffs
[
pointer
+
1
][
0
],
bestEquality2
)
else
:
del
diffs
[
pointer
+
1
]
pointer
-=
1
pointer
+=
1
# Define some regex patterns for matching boundaries.
BLANKLINEEND
=
re
.
compile
(
r"\n\r?\n$"
)
BLANKLINESTART
=
re
.
compile
(
r"^\r?\n\r?\n"
)
def
diff_cleanupEfficiency
(
self
,
diffs
):
"""Reduce the number of edits by eliminating operationally trivial
equalities.
Args:
diffs: Array of diff tuples.
"""
changes
=
False
equalities
=
[]
# Stack of indices where equalities are found.
lastEquality
=
None
# Always equal to diffs[equalities[-1]][1]
pointer
=
0
# Index of current position.
pre_ins
=
False
# Is there an insertion operation before the last equality.
pre_del
=
False
# Is there a deletion operation before the last equality.
post_ins
=
False
# Is there an insertion operation after the last equality.
post_del
=
False
# Is there a deletion operation after the last equality.
while
pointer
<
len
(
diffs
):
if
diffs
[
pointer
][
0
]
==
self
.
DIFF_EQUAL
:
# Equality found.
if
(
len
(
diffs
[
pointer
][
1
])
<
self
.
Diff_EditCost
and
(
post_ins
or
post_del
)):
# Candidate found.
equalities
.
append
(
pointer
)
pre_ins
=
post_ins
pre_del
=
post_del
lastEquality
=
diffs
[
pointer
][
1
]
else
:
# Not a candidate, and can never become one.
equalities
=
[]
lastEquality
=
None
post_ins
=
post_del
=
False
else
:
# An insertion or deletion.
if
diffs
[
pointer
][
0
]
==
self
.
DIFF_DELETE
:
post_del
=
True
else
:
post_ins
=
True
# Five types to be split:
# <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
# <ins>A</ins>X<ins>C</ins><del>D</del>
# <ins>A</ins><del>B</del>X<ins>C</ins>
# <ins>A</del>X<ins>C</ins><del>D</del>
# <ins>A</ins><del>B</del>X<del>C</del>
if
lastEquality
and
((
pre_ins
and
pre_del
and
post_ins
and
post_del
)
or
((
len
(
lastEquality
)
<
self
.
Diff_EditCost
/
2
)
and
(
pre_ins
+
pre_del
+
post_ins
+
post_del
)
==
3
)):
# Duplicate record.
diffs
.
insert
(
equalities
[
-
1
], (
self
.
DIFF_DELETE
,
lastEquality
))
# Change second copy to insert.
diffs
[
equalities
[
-
1
]
+
1
]
=
(
self
.
DIFF_INSERT
,
diffs
[
equalities
[
-
1
]
+
1
][
1
])
equalities
.
pop
()
# Throw away the equality we just deleted.
lastEquality
=
None
if
pre_ins
and
pre_del
:
# No changes made which could affect previous entry, keep going.
post_ins
=
post_del
=
True
equalities
=
[]
else
:
if
len
(
equalities
):
equalities
.
pop
()
# Throw away the previous equality.
if
len
(
equalities
):
pointer
=
equalities
[
-
1
]
else
:
pointer
=
-
1
post_ins
=
post_del
=
False
changes
=
True
pointer
+=
1
if
changes
:
self
.
diff_cleanupMerge
(
diffs
)
def
diff_cleanupMerge
(
self
,
diffs
):
"""Reorder and merge like edit sections. Merge equalities.
Any edit section can move as long as it doesn't cross an equality.
Args:
diffs: Array of diff tuples.
"""
diffs
.
append
((
self
.
DIFF_EQUAL
,
''
))
# Add a dummy entry at the end.
pointer
=
0
count_delete
=
0
count_insert
=
0
text_delete
=
''
text_insert
=
''
while
pointer
<
len
(
diffs
):
if
diffs
[
pointer
][
0
]
==
self
.
DIFF_INSERT
:
count_insert
+=
1
text_insert
+=
diffs
[
pointer
][
1
]
pointer
+=
1
elif
diffs
[
pointer
][
0
]
==
self
.
DIFF_DELETE
:
count_delete
+=
1
text_delete
+=
diffs
[
pointer
][
1
]
pointer
+=
1
elif
diffs
[
pointer
][
0
]
==
self
.
DIFF_EQUAL
:
# Upon reaching an equality, check for prior redundancies.
if
count_delete
+
count_insert
>
1
:
if
count_delete
!=
0
and
count_insert
!=
0
:
# Factor out any common prefixies.
commonlength
=
self
.
diff_commonPrefix
(
text_insert
,
text_delete
)
if
commonlength
!=
0
:
x
=
pointer
-
count_delete
-
count_insert
-
1
if
x
>=
0
and
diffs
[
x
][
0
]
==
self
.
DIFF_EQUAL
:
diffs
[
x
]
=
(
diffs
[
x
][
0
],
diffs
[
x
][
1
]
+
text_insert
[:
commonlength
])
else
:
diffs
.
insert
(
0
, (
self
.
DIFF_EQUAL
,
text_insert
[:
commonlength
]))
pointer
+=
1
text_insert
=
text_insert
[
commonlength
:]
text_delete
=
text_delete
[
commonlength
:]
# Factor out any common suffixies.
commonlength
=
self
.
diff_commonSuffix
(
text_insert
,
text_delete
)
if
commonlength
!=
0
:
diffs
[
pointer
]
=
(
diffs
[
pointer
][
0
],
text_insert
[
-
commonlength
:]
+
diffs
[
pointer
][
1
])
text_insert
=
text_insert
[:
-
commonlength
]
text_delete
=
text_delete
[:
-
commonlength
]
# Delete the offending records and add the merged ones.
new_ops
=
[]
if
len
(
text_delete
)
!=
0
:
new_ops
.
append
((
self
.
DIFF_DELETE
,
text_delete
))
if
len
(
text_insert
)
!=
0
:
new_ops
.
append
((
self
.
DIFF_INSERT
,
text_insert
))
pointer
-=
count_delete
+
count_insert
diffs
[
pointer
:
pointer
+
count_delete
+
count_insert
]
=
new_ops
pointer
+=
len
(
new_ops
)
+
1
elif
pointer
!=
0
and
diffs
[
pointer
-
1
][
0
]
==
self
.
DIFF_EQUAL
:
# Merge this equality with the previous one.
diffs
[
pointer
-
1
]
=
(
diffs
[
pointer
-
1
][
0
],
diffs
[
pointer
-
1
][
1
]
+
diffs
[
pointer
][
1
])
del
diffs
[
pointer
]
else
:
pointer
+=
1
count_insert
=
0
count_delete
=
0
text_delete
=
''
text_insert
=
''
if
diffs
[
-
1
][
1
]
==
''
:
diffs
.
pop
()
# Remove the dummy entry at the end.
# Second pass: look for single edits surrounded on both sides by equalities
# which can be shifted sideways to eliminate an equality.
# e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
changes
=
False
pointer
=
1
# Intentionally ignore the first and last element (don't need checking).
while
pointer
<
len
(
diffs
)
-
1
:
if
(
diffs
[
pointer
-
1
][
0
]
==
self
.
DIFF_EQUAL
and
diffs
[
pointer
+
1
][
0
]
==
self
.
DIFF_EQUAL
):
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