Upload diff_match_patch.py

diff_match_patch.py

@@ -0,0 +1,1907 @@
+#!/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__ = '[email protected] (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):
+        # This is a single edit surrounded by equalities.
+        if diffs[pointer][1].endswith(diffs[pointer - 1][1]):
+          # Shift the edit over the previous equality.
+          if diffs[pointer - 1][1] != "":
+            diffs[pointer] = (diffs[pointer][0],
+                diffs[pointer - 1][1] +
+                diffs[pointer][1][:-len(diffs[pointer - 1][1])])
+            diffs[pointer + 1] = (diffs[pointer + 1][0],
+                                  diffs[pointer - 1][1] + diffs[pointer + 1][1])
+          del diffs[pointer - 1]
+          changes = True
+        elif diffs[pointer][1].startswith(diffs[pointer + 1][1]):
+          # Shift the edit over the next equality.
+          diffs[pointer - 1] = (diffs[pointer - 1][0],
+                                diffs[pointer - 1][1] + diffs[pointer + 1][1])
+          diffs[pointer] = (diffs[pointer][0],
+              diffs[pointer][1][len(diffs[pointer + 1][1]):] +
+              diffs[pointer + 1][1])
+          del diffs[pointer + 1]
+          changes = True
+      pointer += 1
+
+    # If shifts were made, the diff needs reordering and another shift sweep.
+    if changes:
+      self.diff_cleanupMerge(diffs)
+
+  def diff_xIndex(self, diffs, loc):
+    """loc is a location in text1, compute and return the equivalent location
+    in text2.  e.g. "The cat" vs "The big cat", 1->1, 5->8
+
+    Args:
+      diffs: Array of diff tuples.
+      loc: Location within text1.
+
+    Returns:
+      Location within text2.
+    """
+    chars1 = 0
+    chars2 = 0
+    last_chars1 = 0
+    last_chars2 = 0
+    for x in range(len(diffs)):
+      (op, text) = diffs[x]
+      if op != self.DIFF_INSERT:  # Equality or deletion.
+        chars1 += len(text)
+      if op != self.DIFF_DELETE:  # Equality or insertion.
+        chars2 += len(text)
+      if chars1 > loc:  # Overshot the location.
+        break
+      last_chars1 = chars1
+      last_chars2 = chars2
+
+    if len(diffs) != x and diffs[x][0] == self.DIFF_DELETE:
+      # The location was deleted.
+      return last_chars2
+    # Add the remaining len(character).
+    return last_chars2 + (loc - last_chars1)
+
+  def diff_prettyHtml(self, diffs):
+    """Convert a diff array into a pretty HTML report.
+
+    Args:
+      diffs: Array of diff tuples.
+
+    Returns:
+      HTML representation.
+    """
+    html = []
+    for (op, data) in diffs:
+      text = (data.replace("&", "&amp;").replace("<", "&lt;")
+                 .replace(">", "&gt;").replace("\n", "&para;<br>"))
+      if op == self.DIFF_INSERT:
+        html.append("<ins style=\"background:#e6ffe6;\">%s</ins>" % text)
+      elif op == self.DIFF_DELETE:
+        html.append("<del style=\"background:#ffe6e6;\">%s</del>" % text)
+      elif op == self.DIFF_EQUAL:
+        html.append("<span>%s</span>" % text)
+    return "".join(html)
+
+  def diff_text1(self, diffs):
+    """Compute and return the source text (all equalities and deletions).
+
+    Args:
+      diffs: Array of diff tuples.
+
+    Returns:
+      Source text.
+    """
+    text = []
+    for (op, data) in diffs:
+      if op != self.DIFF_INSERT:
+        text.append(data)
+    return "".join(text)
+
+  def diff_text2(self, diffs):
+    """Compute and return the destination text (all equalities and insertions).
+
+    Args:
+      diffs: Array of diff tuples.
+
+    Returns:
+      Destination text.
+    """
+    text = []
+    for (op, data) in diffs:
+      if op != self.DIFF_DELETE:
+        text.append(data)
+    return "".join(text)
+
+  def diff_levenshtein(self, diffs):
+    """Compute the Levenshtein distance; the number of inserted, deleted or
+    substituted characters.
+
+    Args:
+      diffs: Array of diff tuples.
+
+    Returns:
+      Number of changes.
+    """
+    levenshtein = 0
+    insertions = 0
+    deletions = 0
+    for (op, data) in diffs:
+      if op == self.DIFF_INSERT:
+        insertions += len(data)
+      elif op == self.DIFF_DELETE:
+        deletions += len(data)
+      elif op == self.DIFF_EQUAL:
+        # A deletion and an insertion is one substitution.
+        levenshtein += max(insertions, deletions)
+        insertions = 0
+        deletions = 0
+    levenshtein += max(insertions, deletions)
+    return levenshtein
+
+  def diff_toDelta(self, diffs):
+    """Crush the diff into an encoded string which describes the operations
+    required to transform text1 into text2.
+    E.g. =3\t-2\t+ing  -> Keep 3 chars, delete 2 chars, insert 'ing'.
+    Operations are tab-separated.  Inserted text is escaped using %xx notation.
+
+    Args:
+      diffs: Array of diff tuples.
+
+    Returns:
+      Delta text.
+    """
+    text = []
+    for (op, data) in diffs:
+      if op == self.DIFF_INSERT:
+        # High ascii will raise UnicodeDecodeError.  Use Unicode instead.
+        data = data.encode("utf-8")
+        text.append("+" + urllib.parse.quote(data, "!~*'();/?:@&=+$,# "))
+      elif op == self.DIFF_DELETE:
+        text.append("-%d" % len(data))
+      elif op == self.DIFF_EQUAL:
+        text.append("=%d" % len(data))
+    return "\t".join(text)
+
+  def diff_fromDelta(self, text1, delta):
+    """Given the original text1, and an encoded string which describes the
+    operations required to transform text1 into text2, compute the full diff.
+
+    Args:
+      text1: Source string for the diff.
+      delta: Delta text.
+
+    Returns:
+      Array of diff tuples.
+
+    Raises:
+      ValueError: If invalid input.
+    """
+    diffs = []
+    pointer = 0  # Cursor in text1
+    tokens = delta.split("\t")
+    for token in tokens:
+      if token == "":
+        # Blank tokens are ok (from a trailing \t).
+        continue
+      # Each token begins with a one character parameter which specifies the
+      # operation of this token (delete, insert, equality).
+      param = token[1:]
+      if token[0] == "+":
+        param = urllib.parse.unquote(param)
+        diffs.append((self.DIFF_INSERT, param))
+      elif token[0] == "-" or token[0] == "=":
+        try:
+          n = int(param)
+        except ValueError:
+          raise ValueError("Invalid number in diff_fromDelta: " + param)
+        if n < 0:
+          raise ValueError("Negative number in diff_fromDelta: " + param)
+        text = text1[pointer : pointer + n]
+        pointer += n
+        if token[0] == "=":
+          diffs.append((self.DIFF_EQUAL, text))
+        else:
+          diffs.append((self.DIFF_DELETE, text))
+      else:
+        # Anything else is an error.
+        raise ValueError("Invalid diff operation in diff_fromDelta: " +
+            token[0])
+    if pointer != len(text1):
+      raise ValueError(
+          "Delta length (%d) does not equal source text length (%d)." %
+         (pointer, len(text1)))
+    return diffs
+
+  #  MATCH FUNCTIONS
+
+  def match_main(self, text, pattern, loc):
+    """Locate the best instance of 'pattern' in 'text' near 'loc'.
+
+    Args:
+      text: The text to search.
+      pattern: The pattern to search for.
+      loc: The location to search around.
+
+    Returns:
+      Best match index or -1.
+    """
+    # Check for null inputs.
+    if text == None or pattern == None:
+      raise ValueError("Null inputs. (match_main)")
+
+    loc = max(0, min(loc, len(text)))
+    if text == pattern:
+      # Shortcut (potentially not guaranteed by the algorithm)
+      return 0
+    elif not text:
+      # Nothing to match.
+      return -1
+    elif text[loc:loc + len(pattern)] == pattern:
+      # Perfect match at the perfect spot!  (Includes case of null pattern)
+      return loc
+    else:
+      # Do a fuzzy compare.
+      match = self.match_bitap(text, pattern, loc)
+      return match
+
+  def match_bitap(self, text, pattern, loc):
+    """Locate the best instance of 'pattern' in 'text' near 'loc' using the
+    Bitap algorithm.
+
+    Args:
+      text: The text to search.
+      pattern: The pattern to search for.
+      loc: The location to search around.
+
+    Returns:
+      Best match index or -1.
+    """
+    # Python doesn't have a maxint limit, so ignore this check.
+    #if self.Match_MaxBits != 0 and len(pattern) > self.Match_MaxBits:
+    #  raise ValueError("Pattern too long for this application.")
+
+    # Initialise the alphabet.
+    s = self.match_alphabet(pattern)
+
+    def match_bitapScore(e, x):
+      """Compute and return the score for a match with e errors and x location.
+      Accesses loc and pattern through being a closure.
+
+      Args:
+        e: Number of errors in match.
+        x: Location of match.
+
+      Returns:
+        Overall score for match (0.0 = good, 1.0 = bad).
+      """
+      accuracy = float(e) / len(pattern)
+      proximity = abs(loc - x)
+      if not self.Match_Distance:
+        # Dodge divide by zero error.
+        return proximity and 1.0 or accuracy
+      return accuracy + (proximity / float(self.Match_Distance))
+
+    # Highest score beyond which we give up.
+    score_threshold = self.Match_Threshold
+    # Is there a nearby exact match? (speedup)
+    best_loc = text.find(pattern, loc)
+    if best_loc != -1:
+      score_threshold = min(match_bitapScore(0, best_loc), score_threshold)
+      # What about in the other direction? (speedup)
+      best_loc = text.rfind(pattern, loc + len(pattern))
+      if best_loc != -1:
+        score_threshold = min(match_bitapScore(0, best_loc), score_threshold)
+
+    # Initialise the bit arrays.
+    matchmask = 1 << (len(pattern) - 1)
+    best_loc = -1
+
+    bin_max = len(pattern) + len(text)
+    # Empty initialization added to appease pychecker.
+    last_rd = None
+    for d in range(len(pattern)):
+      # Scan for the best match each iteration allows for one more error.
+      # Run a binary search to determine how far from 'loc' we can stray at
+      # this error level.
+      bin_min = 0
+      bin_mid = bin_max
+      while bin_min < bin_mid:
+        if match_bitapScore(d, loc + bin_mid) <= score_threshold:
+          bin_min = bin_mid
+        else:
+          bin_max = bin_mid
+        bin_mid = (bin_max - bin_min) // 2 + bin_min
+
+      # Use the result from this iteration as the maximum for the next.
+      bin_max = bin_mid
+      start = max(1, loc - bin_mid + 1)
+      finish = min(loc + bin_mid, len(text)) + len(pattern)
+
+      rd = [0] * (finish + 2)
+      rd[finish + 1] = (1 << d) - 1
+      for j in range(finish, start - 1, -1):
+        if len(text) <= j - 1:
+          # Out of range.
+          charMatch = 0
+        else:
+          charMatch = s.get(text[j - 1], 0)
+        if d == 0:  # First pass: exact match.
+          rd[j] = ((rd[j + 1] << 1) | 1) & charMatch
+        else:  # Subsequent passes: fuzzy match.
+          rd[j] = (((rd[j + 1] << 1) | 1) & charMatch) | (
+              ((last_rd[j + 1] | last_rd[j]) << 1) | 1) | last_rd[j + 1]
+        if rd[j] & matchmask:
+          score = match_bitapScore(d, j - 1)
+          # This match will almost certainly be better than any existing match.
+          # But check anyway.
+          if score <= score_threshold:
+            # Told you so.
+            score_threshold = score
+            best_loc = j - 1
+            if best_loc > loc:
+              # When passing loc, don't exceed our current distance from loc.
+              start = max(1, 2 * loc - best_loc)
+            else:
+              # Already passed loc, downhill from here on in.
+              break
+      # No hope for a (better) match at greater error levels.
+      if match_bitapScore(d + 1, loc) > score_threshold:
+        break
+      last_rd = rd
+    return best_loc
+
+  def match_alphabet(self, pattern):
+    """Initialise the alphabet for the Bitap algorithm.
+
+    Args:
+      pattern: The text to encode.
+
+    Returns:
+      Hash of character locations.
+    """
+    s = {}
+    for char in pattern:
+      s[char] = 0
+    for i in range(len(pattern)):
+      s[pattern[i]] |= 1 << (len(pattern) - i - 1)
+    return s
+
+  #  PATCH FUNCTIONS
+
+  def patch_addContext(self, patch, text):
+    """Increase the context until it is unique,
+    but don't let the pattern expand beyond Match_MaxBits.
+
+    Args:
+      patch: The patch to grow.
+      text: Source text.
+    """
+    if len(text) == 0:
+      return
+    pattern = text[patch.start2 : patch.start2 + patch.length1]
+    padding = 0
+
+    # Look for the first and last matches of pattern in text.  If two different
+    # matches are found, increase the pattern length.
+    while (text.find(pattern) != text.rfind(pattern) and (self.Match_MaxBits ==
+        0 or len(pattern) < self.Match_MaxBits - self.Patch_Margin -
+        self.Patch_Margin)):
+      padding += self.Patch_Margin
+      pattern = text[max(0, patch.start2 - padding) :
+                     patch.start2 + patch.length1 + padding]
+    # Add one chunk for good luck.
+    padding += self.Patch_Margin
+
+    # Add the prefix.
+    prefix = text[max(0, patch.start2 - padding) : patch.start2]
+    if prefix:
+      patch.diffs[:0] = [(self.DIFF_EQUAL, prefix)]
+    # Add the suffix.
+    suffix = text[patch.start2 + patch.length1 :
+                  patch.start2 + patch.length1 + padding]
+    if suffix:
+      patch.diffs.append((self.DIFF_EQUAL, suffix))
+
+    # Roll back the start points.
+    patch.start1 -= len(prefix)
+    patch.start2 -= len(prefix)
+    # Extend lengths.
+    patch.length1 += len(prefix) + len(suffix)
+    patch.length2 += len(prefix) + len(suffix)
+
+  def patch_make(self, a, b=None, c=None):
+    """Compute a list of patches to turn text1 into text2.
+    Use diffs if provided, otherwise compute it ourselves.
+    There are four ways to call this function, depending on what data is
+    available to the caller:
+    Method 1:
+    a = text1, b = text2
+    Method 2:
+    a = diffs
+    Method 3 (optimal):
+    a = text1, b = diffs
+    Method 4 (deprecated, use method 3):
+    a = text1, b = text2, c = diffs
+
+    Args:
+      a: text1 (methods 1,3,4) or Array of diff tuples for text1 to
+          text2 (method 2).
+      b: text2 (methods 1,4) or Array of diff tuples for text1 to
+          text2 (method 3) or undefined (method 2).
+      c: Array of diff tuples for text1 to text2 (method 4) or
+          undefined (methods 1,2,3).
+
+    Returns:
+      Array of Patch objects.
+    """
+    text1 = None
+    diffs = None
+    if isinstance(a, str) and isinstance(b, str) and c is None:
+      # Method 1: text1, text2
+      # Compute diffs from text1 and text2.
+      text1 = a
+      diffs = self.diff_main(text1, b, True)
+      if len(diffs) > 2:
+        self.diff_cleanupSemantic(diffs)
+        self.diff_cleanupEfficiency(diffs)
+    elif isinstance(a, list) and b is None and c is None:
+      # Method 2: diffs
+      # Compute text1 from diffs.
+      diffs = a
+      text1 = self.diff_text1(diffs)
+    elif isinstance(a, str) and isinstance(b, list) and c is None:
+      # Method 3: text1, diffs
+      text1 = a
+      diffs = b
+    elif (isinstance(a, str) and isinstance(b, str) and
+          isinstance(c, list)):
+      # Method 4: text1, text2, diffs
+      # text2 is not used.
+      text1 = a
+      diffs = c
+    else:
+      raise ValueError("Unknown call format to patch_make.")
+
+    if not diffs:
+      return []  # Get rid of the None case.
+    patches = []
+    patch = patch_obj()
+    char_count1 = 0  # Number of characters into the text1 string.
+    char_count2 = 0  # Number of characters into the text2 string.
+    prepatch_text = text1  # Recreate the patches to determine context info.
+    postpatch_text = text1
+    for x in range(len(diffs)):
+      (diff_type, diff_text) = diffs[x]
+      if len(patch.diffs) == 0 and diff_type != self.DIFF_EQUAL:
+        # A new patch starts here.
+        patch.start1 = char_count1
+        patch.start2 = char_count2
+      if diff_type == self.DIFF_INSERT:
+        # Insertion
+        patch.diffs.append(diffs[x])
+        patch.length2 += len(diff_text)
+        postpatch_text = (postpatch_text[:char_count2] + diff_text +
+                          postpatch_text[char_count2:])
+      elif diff_type == self.DIFF_DELETE:
+        # Deletion.
+        patch.length1 += len(diff_text)
+        patch.diffs.append(diffs[x])
+        postpatch_text = (postpatch_text[:char_count2] +
+                          postpatch_text[char_count2 + len(diff_text):])
+      elif (diff_type == self.DIFF_EQUAL and
+            len(diff_text) <= 2 * self.Patch_Margin and
+            len(patch.diffs) != 0 and len(diffs) != x + 1):
+        # Small equality inside a patch.
+        patch.diffs.append(diffs[x])
+        patch.length1 += len(diff_text)
+        patch.length2 += len(diff_text)
+
+      if (diff_type == self.DIFF_EQUAL and
+          len(diff_text) >= 2 * self.Patch_Margin):
+        # Time for a new patch.
+        if len(patch.diffs) != 0:
+          self.patch_addContext(patch, prepatch_text)
+          patches.append(patch)
+          patch = patch_obj()
+          # Unlike Unidiff, our patch lists have a rolling context.
+          # https://github.com/google/diff-match-patch/wiki/Unidiff
+          # Update prepatch text & pos to reflect the application of the
+          # just completed patch.
+          prepatch_text = postpatch_text
+          char_count1 = char_count2
+
+      # Update the current character count.
+      if diff_type != self.DIFF_INSERT:
+        char_count1 += len(diff_text)
+      if diff_type != self.DIFF_DELETE:
+        char_count2 += len(diff_text)
+
+    # Pick up the leftover patch if not empty.
+    if len(patch.diffs) != 0:
+      self.patch_addContext(patch, prepatch_text)
+      patches.append(patch)
+    return patches
+
+  def patch_deepCopy(self, patches):
+    """Given an array of patches, return another array that is identical.
+
+    Args:
+      patches: Array of Patch objects.
+
+    Returns:
+      Array of Patch objects.
+    """
+    patchesCopy = []
+    for patch in patches:
+      patchCopy = patch_obj()
+      # No need to deep copy the tuples since they are immutable.
+      patchCopy.diffs = patch.diffs[:]
+      patchCopy.start1 = patch.start1
+      patchCopy.start2 = patch.start2
+      patchCopy.length1 = patch.length1
+      patchCopy.length2 = patch.length2
+      patchesCopy.append(patchCopy)
+    return patchesCopy
+
+  def patch_apply(self, patches, text):
+    """Merge a set of patches onto the text.  Return a patched text, as well
+    as a list of true/false values indicating which patches were applied.
+
+    Args:
+      patches: Array of Patch objects.
+      text: Old text.
+
+    Returns:
+      Two element Array, containing the new text and an array of boolean values.
+    """
+    if not patches:
+      return (text, [])
+
+    # Deep copy the patches so that no changes are made to originals.
+    patches = self.patch_deepCopy(patches)
+
+    nullPadding = self.patch_addPadding(patches)
+    text = nullPadding + text + nullPadding
+    self.patch_splitMax(patches)
+
+    # delta keeps track of the offset between the expected and actual location
+    # of the previous patch.  If there are patches expected at positions 10 and
+    # 20, but the first patch was found at 12, delta is 2 and the second patch
+    # has an effective expected position of 22.
+    delta = 0
+    results = []
+    for patch in patches:
+      expected_loc = patch.start2 + delta
+      text1 = self.diff_text1(patch.diffs)
+      end_loc = -1
+      if len(text1) > self.Match_MaxBits:
+        # patch_splitMax will only provide an oversized pattern in the case of
+        # a monster delete.
+        start_loc = self.match_main(text, text1[:self.Match_MaxBits],
+                                    expected_loc)
+        if start_loc != -1:
+          end_loc = self.match_main(text, text1[-self.Match_MaxBits:],
+              expected_loc + len(text1) - self.Match_MaxBits)
+          if end_loc == -1 or start_loc >= end_loc:
+            # Can't find valid trailing context.  Drop this patch.
+            start_loc = -1
+      else:
+        start_loc = self.match_main(text, text1, expected_loc)
+      if start_loc == -1:
+        # No match found.  :(
+        results.append(False)
+        # Subtract the delta for this failed patch from subsequent patches.
+        delta -= patch.length2 - patch.length1
+      else:
+        # Found a match.  :)
+        results.append(True)
+        delta = start_loc - expected_loc
+        if end_loc == -1:
+          text2 = text[start_loc : start_loc + len(text1)]
+        else:
+          text2 = text[start_loc : end_loc + self.Match_MaxBits]
+        if text1 == text2:
+          # Perfect match, just shove the replacement text in.
+          text = (text[:start_loc] + self.diff_text2(patch.diffs) +
+                      text[start_loc + len(text1):])
+        else:
+          # Imperfect match.
+          # Run a diff to get a framework of equivalent indices.
+          diffs = self.diff_main(text1, text2, False)
+          if (len(text1) > self.Match_MaxBits and
+              self.diff_levenshtein(diffs) / float(len(text1)) >
+              self.Patch_DeleteThreshold):
+            # The end points match, but the content is unacceptably bad.
+            results[-1] = False
+          else:
+            self.diff_cleanupSemanticLossless(diffs)
+            index1 = 0
+            for (op, data) in patch.diffs:
+              if op != self.DIFF_EQUAL:
+                index2 = self.diff_xIndex(diffs, index1)
+              if op == self.DIFF_INSERT:  # Insertion
+                text = text[:start_loc + index2] + data + text[start_loc +
+                                                               index2:]
+              elif op == self.DIFF_DELETE:  # Deletion
+                text = text[:start_loc + index2] + text[start_loc +
+                    self.diff_xIndex(diffs, index1 + len(data)):]
+              if op != self.DIFF_DELETE:
+                index1 += len(data)
+    # Strip the padding off.
+    text = text[len(nullPadding):-len(nullPadding)]
+    return (text, results)
+
+  def patch_addPadding(self, patches):
+    """Add some padding on text start and end so that edges can match
+    something.  Intended to be called only from within patch_apply.
+
+    Args:
+      patches: Array of Patch objects.
+
+    Returns:
+      The padding string added to each side.
+    """
+    paddingLength = self.Patch_Margin
+    nullPadding = ""
+    for x in range(1, paddingLength + 1):
+      nullPadding += chr(x)
+
+    # Bump all the patches forward.
+    for patch in patches:
+      patch.start1 += paddingLength
+      patch.start2 += paddingLength
+
+    # Add some padding on start of first diff.
+    patch = patches[0]
+    diffs = patch.diffs
+    if not diffs or diffs[0][0] != self.DIFF_EQUAL:
+      # Add nullPadding equality.
+      diffs.insert(0, (self.DIFF_EQUAL, nullPadding))
+      patch.start1 -= paddingLength  # Should be 0.
+      patch.start2 -= paddingLength  # Should be 0.
+      patch.length1 += paddingLength
+      patch.length2 += paddingLength
+    elif paddingLength > len(diffs[0][1]):
+      # Grow first equality.
+      extraLength = paddingLength - len(diffs[0][1])
+      newText = nullPadding[len(diffs[0][1]):] + diffs[0][1]
+      diffs[0] = (diffs[0][0], newText)
+      patch.start1 -= extraLength
+      patch.start2 -= extraLength
+      patch.length1 += extraLength
+      patch.length2 += extraLength
+
+    # Add some padding on end of last diff.
+    patch = patches[-1]
+    diffs = patch.diffs
+    if not diffs or diffs[-1][0] != self.DIFF_EQUAL:
+      # Add nullPadding equality.
+      diffs.append((self.DIFF_EQUAL, nullPadding))
+      patch.length1 += paddingLength
+      patch.length2 += paddingLength
+    elif paddingLength > len(diffs[-1][1]):
+      # Grow last equality.
+      extraLength = paddingLength - len(diffs[-1][1])
+      newText = diffs[-1][1] + nullPadding[:extraLength]
+      diffs[-1] = (diffs[-1][0], newText)
+      patch.length1 += extraLength
+      patch.length2 += extraLength
+
+    return nullPadding
+
+  def patch_splitMax(self, patches):
+    """Look through the patches and break up any which are longer than the
+    maximum limit of the match algorithm.
+    Intended to be called only from within patch_apply.
+
+    Args:
+      patches: Array of Patch objects.
+    """
+    patch_size = self.Match_MaxBits
+    if patch_size == 0:
+      # Python has the option of not splitting strings due to its ability
+      # to handle integers of arbitrary precision.
+      return
+    for x in range(len(patches)):
+      if patches[x].length1 <= patch_size:
+        continue
+      bigpatch = patches[x]
+      # Remove the big old patch.
+      del patches[x]
+      x -= 1
+      start1 = bigpatch.start1
+      start2 = bigpatch.start2
+      precontext = ''
+      while len(bigpatch.diffs) != 0:
+        # Create one of several smaller patches.
+        patch = patch_obj()
+        empty = True
+        patch.start1 = start1 - len(precontext)
+        patch.start2 = start2 - len(precontext)
+        if precontext:
+          patch.length1 = patch.length2 = len(precontext)
+          patch.diffs.append((self.DIFF_EQUAL, precontext))
+
+        while (len(bigpatch.diffs) != 0 and
+               patch.length1 < patch_size - self.Patch_Margin):
+          (diff_type, diff_text) = bigpatch.diffs[0]
+          if diff_type == self.DIFF_INSERT:
+            # Insertions are harmless.
+            patch.length2 += len(diff_text)
+            start2 += len(diff_text)
+            patch.diffs.append(bigpatch.diffs.pop(0))
+            empty = False
+          elif (diff_type == self.DIFF_DELETE and len(patch.diffs) == 1 and
+              patch.diffs[0][0] == self.DIFF_EQUAL and
+              len(diff_text) > 2 * patch_size):
+            # This is a large deletion.  Let it pass in one chunk.
+            patch.length1 += len(diff_text)
+            start1 += len(diff_text)
+            empty = False
+            patch.diffs.append((diff_type, diff_text))
+            del bigpatch.diffs[0]
+          else:
+            # Deletion or equality.  Only take as much as we can stomach.
+            diff_text = diff_text[:patch_size - patch.length1 -
+                                  self.Patch_Margin]
+            patch.length1 += len(diff_text)
+            start1 += len(diff_text)
+            if diff_type == self.DIFF_EQUAL:
+              patch.length2 += len(diff_text)
+              start2 += len(diff_text)
+            else:
+              empty = False
+
+            patch.diffs.append((diff_type, diff_text))
+            if diff_text == bigpatch.diffs[0][1]:
+              del bigpatch.diffs[0]
+            else:
+              bigpatch.diffs[0] = (bigpatch.diffs[0][0],
+                                   bigpatch.diffs[0][1][len(diff_text):])
+
+        # Compute the head context for the next patch.
+        precontext = self.diff_text2(patch.diffs)
+        precontext = precontext[-self.Patch_Margin:]
+        # Append the end context for this patch.
+        postcontext = self.diff_text1(bigpatch.diffs)[:self.Patch_Margin]
+        if postcontext:
+          patch.length1 += len(postcontext)
+          patch.length2 += len(postcontext)
+          if len(patch.diffs) != 0 and patch.diffs[-1][0] == self.DIFF_EQUAL:
+            patch.diffs[-1] = (self.DIFF_EQUAL, patch.diffs[-1][1] +
+                               postcontext)
+          else:
+            patch.diffs.append((self.DIFF_EQUAL, postcontext))
+
+        if not empty:
+          x += 1
+          patches.insert(x, patch)
+
+  def patch_toText(self, patches):
+    """Take a list of patches and return a textual representation.
+
+    Args:
+      patches: Array of Patch objects.
+
+    Returns:
+      Text representation of patches.
+    """
+    text = []
+    for patch in patches:
+      text.append(str(patch))
+    return "".join(text)
+
+  def patch_fromText(self, textline):
+    """Parse a textual representation of patches and return a list of patch
+    objects.
+
+    Args:
+      textline: Text representation of patches.
+
+    Returns:
+      Array of Patch objects.
+
+    Raises:
+      ValueError: If invalid input.
+    """
+    patches = []
+    if not textline:
+      return patches
+    text = textline.split('\n')
+    while len(text) != 0:
+      m = re.match(r"^@@ -(\d+),?(\d*) \+(\d+),?(\d*) @@$", text[0])
+      if not m:
+        raise ValueError("Invalid patch string: " + text[0])
+      patch = patch_obj()
+      patches.append(patch)
+      patch.start1 = int(m.group(1))
+      if m.group(2) == '':
+        patch.start1 -= 1
+        patch.length1 = 1
+      elif m.group(2) == '0':
+        patch.length1 = 0
+      else:
+        patch.start1 -= 1
+        patch.length1 = int(m.group(2))
+
+      patch.start2 = int(m.group(3))
+      if m.group(4) == '':
+        patch.start2 -= 1
+        patch.length2 = 1
+      elif m.group(4) == '0':
+        patch.length2 = 0
+      else:
+        patch.start2 -= 1
+        patch.length2 = int(m.group(4))
+
+      del text[0]
+
+      while len(text) != 0:
+        if text[0]:
+          sign = text[0][0]
+        else:
+          sign = ''
+        line = urllib.parse.unquote(text[0][1:])
+        if sign == '+':
+          # Insertion.
+          patch.diffs.append((self.DIFF_INSERT, line))
+        elif sign == '-':
+          # Deletion.
+          patch.diffs.append((self.DIFF_DELETE, line))
+        elif sign == ' ':
+          # Minor equality.
+          patch.diffs.append((self.DIFF_EQUAL, line))
+        elif sign == '@':
+          # Start of next patch.
+          break
+        elif sign == '':
+          # Blank line?  Whatever.
+          pass
+        else:
+          # WTF?
+          raise ValueError("Invalid patch mode: '%s'\n%s" % (sign, line))
+        del text[0]
+    return patches
+
+
+class patch_obj:
+  """Class representing one patch operation.
+  """
+
+  def __init__(self):
+    """Initializes with an empty list of diffs.
+    """
+    self.diffs = []
+    self.start1 = None
+    self.start2 = None
+    self.length1 = 0
+    self.length2 = 0
+
+  def __str__(self):
+    """Emulate GNU diff's format.
+    Header: @@ -382,8 +481,9 @@
+    Indices are printed as 1-based, not 0-based.
+
+    Returns:
+      The GNU diff string.
+    """
+    if self.length1 == 0:
+      coords1 = str(self.start1) + ",0"
+    elif self.length1 == 1:
+      coords1 = str(self.start1 + 1)
+    else:
+      coords1 = str(self.start1 + 1) + "," + str(self.length1)
+    if self.length2 == 0:
+      coords2 = str(self.start2) + ",0"
+    elif self.length2 == 1:
+      coords2 = str(self.start2 + 1)
+    else:
+      coords2 = str(self.start2 + 1) + "," + str(self.length2)
+    text = ["@@ -", coords1, " +", coords2, " @@\n"]
+    # Escape the body of the patch with %xx notation.
+    for (op, data) in self.diffs:
+      if op == diff_match_patch.DIFF_INSERT:
+        text.append("+")
+      elif op == diff_match_patch.DIFF_DELETE:
+        text.append("-")
+      elif op == diff_match_patch.DIFF_EQUAL:
+        text.append(" ")
+      # High ascii will raise UnicodeDecodeError.  Use Unicode instead.
+      data = data.encode("utf-8")
+      text.append(urllib.parse.quote(data, "!~*'();/?:@&=+$,# ") + "\n")
+    return "".join(text)