lxml.html.diff

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# Source Code for Module lxml.html.diff

      1  import difflib
      2  from lxml import etree
      3  from lxml.html import fragment_fromstring
      4  import re
      5
      6  __all__ = ['html_annotate', 'htmldiff']
      7
      8  try:
      9      from html import escape as html_escape
     10  except ImportError:
     11      from cgi import escape as html_escape
     12  try:
     13      _unicode = unicode
     14  except NameError:
     15      # Python 3
     16      _unicode = str
     17  try:
     18      basestring
     19  except NameError:
     20      # Python 3
     21      basestring = str
     22
     23  ############################################################
     24  ## Annotation
     25  ############################################################
     26
     27 -def default_markup(text, version):
     28      return '<span title="%s">%s</span>' % (
     29          html_escape(_unicode(version), 1), text)
     30
     31 -def html_annotate(doclist, markup=default_markup):
     32      """
     33      doclist should be ordered from oldest to newest, like::
     34
     35          >>> version1 = 'Hello World'
     36          >>> version2 = 'Goodbye World'
     37          >>> print(html_annotate([(version1, 'version 1'),
     38          ...                      (version2, 'version 2')]))
     39          <span title="version 2">Goodbye</span> <span title="version 1">World</span>
     40
     41      The documents must be *fragments* (str/UTF8 or unicode), not
     42      complete documents
     43
     44      The markup argument is a function to markup the spans of words.
     45      This function is called like markup('Hello', 'version 2'), and
     46      returns HTML.  The first argument is text and never includes any
     47      markup.  The default uses a span with a title:
     48
     49          >>> print(default_markup('Some Text', 'by Joe'))
     50          <span title="by Joe">Some Text</span>
     51      """
     52      # The basic strategy we have is to split the documents up into
     53      # logical tokens (which are words with attached markup).  We then
     54      # do diffs of each of the versions to track when a token first
     55      # appeared in the document; the annotation attached to the token
     56      # is the version where it first appeared.
     57      tokenlist = [tokenize_annotated(doc, version)
     58                   for doc, version in doclist]
     59      cur_tokens = tokenlist[0]
     60      for tokens in tokenlist[1:]:
     61          html_annotate_merge_annotations(cur_tokens, tokens)
     62          cur_tokens = tokens
     63
     64      # After we've tracked all the tokens, we can combine spans of text
     65      # that are adjacent and have the same annotation
     66      cur_tokens = compress_tokens(cur_tokens)
     67      # And finally add markup
     68      result = markup_serialize_tokens(cur_tokens, markup)
     69      return ''.join(result).strip()
     70
     71 -def tokenize_annotated(doc, annotation):
     72      """Tokenize a document and add an annotation attribute to each token
     73      """
     74      tokens = tokenize(doc, include_hrefs=False)
     75      for tok in tokens:
     76          tok.annotation = annotation
     77      return tokens
     78
     79 -def html_annotate_merge_annotations(tokens_old, tokens_new):
     80      """Merge the annotations from tokens_old into tokens_new, when the
     81      tokens in the new document already existed in the old document.
     82      """
     83      s = InsensitiveSequenceMatcher(a=tokens_old, b=tokens_new)
     84      commands = s.get_opcodes()
     85
     86      for command, i1, i2, j1, j2 in commands:
     87          if command == 'equal':
     88              eq_old = tokens_old[i1:i2]
     89              eq_new = tokens_new[j1:j2]
     90              copy_annotations(eq_old, eq_new)
     91
     92 -def copy_annotations(src, dest):
     93      """
     94      Copy annotations from the tokens listed in src to the tokens in dest
     95      """
     96      assert len(src) == len(dest)
     97      for src_tok, dest_tok in zip(src, dest):
     98          dest_tok.annotation = src_tok.annotation
     99
    100 -def compress_tokens(tokens):
    101      """
    102      Combine adjacent tokens when there is no HTML between the tokens,
    103      and they share an annotation
    104      """
    105      result = [tokens[0]]
    106      for tok in tokens[1:]:
    107          if (not result[-1].post_tags and
    108              not tok.pre_tags and
    109              result[-1].annotation == tok.annotation):
    110              compress_merge_back(result, tok)
    111          else:
    112              result.append(tok)
    113      return result
    114
    115 -def compress_merge_back(tokens, tok):
    116      """ Merge tok into the last element of tokens (modifying the list of
    117      tokens in-place).  """
    118      last = tokens[-1]
    119      if type(last) is not token or type(tok) is not token:
    120          tokens.append(tok)
    121      else:
    122          text = _unicode(last)
    123          if last.trailing_whitespace:
    124              text += last.trailing_whitespace
    125          text += tok
    126          merged = token(text,
    127                         pre_tags=last.pre_tags,
    128                         post_tags=tok.post_tags,
    129                         trailing_whitespace=tok.trailing_whitespace)
    130          merged.annotation = last.annotation
    131          tokens[-1] = merged
    132
    133 -def markup_serialize_tokens(tokens, markup_func):
    134      """
    135      Serialize the list of tokens into a list of text chunks, calling
    136      markup_func around text to add annotations.
    137      """
    138      for token in tokens:
    139          for pre in token.pre_tags:
    140              yield pre
    141          html = token.html()
    142          html = markup_func(html, token.annotation)
    143          if token.trailing_whitespace:
    144              html += token.trailing_whitespace
    145          yield html
    146          for post in token.post_tags:
    147              yield post
    148
    149
    150  ############################################################
    151  ## HTML Diffs
    152  ############################################################
    153
    154 -def htmldiff(old_html, new_html):
    155      ## FIXME: this should take parsed documents too, and use their body
    156      ## or other content.
    157      """ Do a diff of the old and new document.  The documents are HTML
    158      *fragments* (str/UTF8 or unicode), they are not complete documents
    159      (i.e., no <html> tag).
    160
    161      Returns HTML with <ins> and <del> tags added around the
    162      appropriate text.
    163
    164      Markup is generally ignored, with the markup from new_html
    165      preserved, and possibly some markup from old_html (though it is
    166      considered acceptable to lose some of the old markup).  Only the
    167      words in the HTML are diffed.  The exception is <img> tags, which
    168      are treated like words, and the href attribute of <a> tags, which
    169      are noted inside the tag itself when there are changes.
    170      """
    171      old_html_tokens = tokenize(old_html)
    172      new_html_tokens = tokenize(new_html)
    173      result = htmldiff_tokens(old_html_tokens, new_html_tokens)
    174      result = ''.join(result).strip()
    175      return fixup_ins_del_tags(result)
    176
    177 -def htmldiff_tokens(html1_tokens, html2_tokens):
    178      """ Does a diff on the tokens themselves, returning a list of text
    179      chunks (not tokens).
    180      """
    181      # There are several passes as we do the differences.  The tokens
    182      # isolate the portion of the content we care to diff; difflib does
    183      # all the actual hard work at that point.
    184      #
    185      # Then we must create a valid document from pieces of both the old
    186      # document and the new document.  We generally prefer to take
    187      # markup from the new document, and only do a best effort attempt
    188      # to keep markup from the old document; anything that we can't
    189      # resolve we throw away.  Also we try to put the deletes as close
    190      # to the location where we think they would have been -- because
    191      # we are only keeping the markup from the new document, it can be
    192      # fuzzy where in the new document the old text would have gone.
    193      # Again we just do a best effort attempt.
    194      s = InsensitiveSequenceMatcher(a=html1_tokens, b=html2_tokens)
    195      commands = s.get_opcodes()
    196      result = []
    197      for command, i1, i2, j1, j2 in commands:
    198          if command == 'equal':
    199              result.extend(expand_tokens(html2_tokens[j1:j2], equal=True))
    200              continue
    201          if command == 'insert' or command == 'replace':
    202              ins_tokens = expand_tokens(html2_tokens[j1:j2])
    203              merge_insert(ins_tokens, result)
    204          if command == 'delete' or command == 'replace':
    205              del_tokens = expand_tokens(html1_tokens[i1:i2])
    206              merge_delete(del_tokens, result)
    207      # If deletes were inserted directly as <del> then we'd have an
    208      # invalid document at this point.  Instead we put in special
    209      # markers, and when the complete diffed document has been created
    210      # we try to move the deletes around and resolve any problems.
    211      result = cleanup_delete(result)
    212
    213      return result
    214
    215 -def expand_tokens(tokens, equal=False):
    216      """Given a list of tokens, return a generator of the chunks of
    217      text for the data in the tokens.
    218      """
    219      for token in tokens:
    220          for pre in token.pre_tags:
    221              yield pre
    222          if not equal or not token.hide_when_equal:
    223              if token.trailing_whitespace:
    224                  yield token.html() + token.trailing_whitespace
    225              else:
    226                  yield token.html()
    227          for post in token.post_tags:
    228              yield post
    229
    230 -def merge_insert(ins_chunks, doc):
    231      """ doc is the already-handled document (as a list of text chunks);
    232      here we add <ins>ins_chunks</ins> to the end of that.  """
    233      # Though we don't throw away unbalanced_start or unbalanced_end
    234      # (we assume there is accompanying markup later or earlier in the
    235      # document), we only put <ins> around the balanced portion.
    236      unbalanced_start, balanced, unbalanced_end = split_unbalanced(ins_chunks)
    237      doc.extend(unbalanced_start)
    238      if doc and not doc[-1].endswith(' '):
    239          # Fix up the case where the word before the insert didn't end with
    240          # a space
    241          doc[-1] += ' '
    242      doc.append('<ins>')
    243      if balanced and balanced[-1].endswith(' '):
    244          # We move space outside of </ins>
    245          balanced[-1] = balanced[-1][:-1]
    246      doc.extend(balanced)
    247      doc.append('</ins> ')
    248      doc.extend(unbalanced_end)
    249
    250  # These are sentinals to represent the start and end of a <del>
    251  # segment, until we do the cleanup phase to turn them into proper
    252  # markup:
    253 -class DEL_START:
    254      pass
    255 -class DEL_END:
    256      pass
    257
    258 -class NoDeletes(Exception):
    259      """ Raised when the document no longer contains any pending deletes
    260      (DEL_START/DEL_END) """
    261
    262 -def merge_delete(del_chunks, doc):
    263      """ Adds the text chunks in del_chunks to the document doc (another
    264      list of text chunks) with marker to show it is a delete.
    265      cleanup_delete later resolves these markers into <del> tags."""
    266      doc.append(DEL_START)
    267      doc.extend(del_chunks)
    268      doc.append(DEL_END)
    269
    270 -def cleanup_delete(chunks):
    271      """ Cleans up any DEL_START/DEL_END markers in the document, replacing
    272      them with <del></del>.  To do this while keeping the document
    273      valid, it may need to drop some tags (either start or end tags).
    274
    275      It may also move the del into adjacent tags to try to move it to a
    276      similar location where it was originally located (e.g., moving a
    277      delete into preceding <div> tag, if the del looks like (DEL_START,
    278      'Text</div>', DEL_END)"""
    279      while 1:
    280          # Find a pending DEL_START/DEL_END, splitting the document
    281          # into stuff-preceding-DEL_START, stuff-inside, and
    282          # stuff-following-DEL_END
    283          try:
    284              pre_delete, delete, post_delete = split_delete(chunks)
    285          except NoDeletes:
    286              # Nothing found, we've cleaned up the entire doc
    287              break
    288          # The stuff-inside-DEL_START/END may not be well balanced
    289          # markup.  First we figure out what unbalanced portions there are:
    290          unbalanced_start, balanced, unbalanced_end = split_unbalanced(delete)
    291          # Then we move the span forward and/or backward based on these
    292          # unbalanced portions:
    293          locate_unbalanced_start(unbalanced_start, pre_delete, post_delete)
    294          locate_unbalanced_end(unbalanced_end, pre_delete, post_delete)
    295          doc = pre_delete
    296          if doc and not doc[-1].endswith(' '):
    297              # Fix up case where the word before us didn't have a trailing space
    298              doc[-1] += ' '
    299          doc.append('<del>')
    300          if balanced and balanced[-1].endswith(' '):
    301              # We move space outside of </del>
    302              balanced[-1] = balanced[-1][:-1]
    303          doc.extend(balanced)
    304          doc.append('</del> ')
    305          doc.extend(post_delete)
    306          chunks = doc
    307      return chunks
    308
    309 -def split_unbalanced(chunks):
    310      """Return (unbalanced_start, balanced, unbalanced_end), where each is
    311      a list of text and tag chunks.
    312
    313      unbalanced_start is a list of all the tags that are opened, but
    314      not closed in this span.  Similarly, unbalanced_end is a list of
    315      tags that are closed but were not opened.  Extracting these might
    316      mean some reordering of the chunks."""
    317      start = []
    318      end = []
    319      tag_stack = []
    320      balanced = []
    321      for chunk in chunks:
    322          if not chunk.startswith('<'):
    323              balanced.append(chunk)
    324              continue
    325          endtag = chunk[1] == '/'
    326          name = chunk.split()[0].strip('<>/')
    327          if name in empty_tags:
    328              balanced.append(chunk)
    329              continue
    330          if endtag:
    331              if tag_stack and tag_stack[-1][0] == name:
    332                  balanced.append(chunk)
    333                  name, pos, tag = tag_stack.pop()
    334                  balanced[pos] = tag
    335              elif tag_stack:
    336                  start.extend([tag for name, pos, tag in tag_stack])
    337                  tag_stack = []
    338                  end.append(chunk)
    339              else:
    340                  end.append(chunk)
    341          else:
    342              tag_stack.append((name, len(balanced), chunk))
    343              balanced.append(None)
    344      start.extend(
    345          [chunk for name, pos, chunk in tag_stack])
    346      balanced = [chunk for chunk in balanced if chunk is not None]
    347      return start, balanced, end
    348
    349 -def split_delete(chunks):
    350      """ Returns (stuff_before_DEL_START, stuff_inside_DEL_START_END,
    351      stuff_after_DEL_END).  Returns the first case found (there may be
    352      more DEL_STARTs in stuff_after_DEL_END).  Raises NoDeletes if
    353      there's no DEL_START found. """
    354      try:
    355          pos = chunks.index(DEL_START)
    356      except ValueError:
    357          raise NoDeletes
    358      pos2 = chunks.index(DEL_END)
    359      return chunks[:pos], chunks[pos+1:pos2], chunks[pos2+1:]
    360
    361 -def locate_unbalanced_start(unbalanced_start, pre_delete, post_delete):
    362      """ pre_delete and post_delete implicitly point to a place in the
    363      document (where the two were split).  This moves that point (by
    364      popping items from one and pushing them onto the other).  It moves
    365      the point to try to find a place where unbalanced_start applies.
    366
    367      As an example::
    368
    369          >>> unbalanced_start = ['<div>']
    370          >>> doc = ['<p>', 'Text', '</p>', '<div>', 'More Text', '</div>']
    371          >>> pre, post = doc[:3], doc[3:]
    372          >>> pre, post
    373          (['<p>', 'Text', '</p>'], ['<div>', 'More Text', '</div>'])
    374          >>> locate_unbalanced_start(unbalanced_start, pre, post)
    375          >>> pre, post
    376          (['<p>', 'Text', '</p>', '<div>'], ['More Text', '</div>'])
    377
    378      As you can see, we moved the point so that the dangling <div> that
    379      we found will be effectively replaced by the div in the original
    380      document.  If this doesn't work out, we just throw away
    381      unbalanced_start without doing anything.
    382      """
    383      while 1:
    384          if not unbalanced_start:
    385              # We have totally succeeded in finding the position
    386              break
    387          finding = unbalanced_start[0]
    388          finding_name = finding.split()[0].strip('<>')
    389          if not post_delete:
    390              break
    391          next = post_delete[0]
    392          if next is DEL_START or not next.startswith('<'):
    393              # Reached a word, we can't move the delete text forward
    394              break
    395          if next[1] == '/':
    396              # Reached a closing tag, can we go further?  Maybe not...
    397              break
    398          name = next.split()[0].strip('<>')
    399          if name == 'ins':
    400              # Can't move into an insert
    401              break
    402          assert name != 'del', (
    403              "Unexpected delete tag: %r" % next)
    404          if name == finding_name:
    405              unbalanced_start.pop(0)
    406              pre_delete.append(post_delete.pop(0))
    407          else:
    408              # Found a tag that doesn't match
    409              break
    410
    411 -def locate_unbalanced_end(unbalanced_end, pre_delete, post_delete):
    412      """ like locate_unbalanced_start, except handling end tags and
    413      possibly moving the point earlier in the document.  """
    414      while 1:
    415          if not unbalanced_end:
    416              # Success
    417              break
    418          finding = unbalanced_end[-1]
    419          finding_name = finding.split()[0].strip('<>/')
    420          if not pre_delete:
    421              break
    422          next = pre_delete[-1]
    423          if next is DEL_END or not next.startswith('</'):
    424              # A word or a start tag
    425              break
    426          name = next.split()[0].strip('<>/')
    427          if name == 'ins' or name == 'del':
    428              # Can't move into an insert or delete
    429              break
    430          if name == finding_name:
    431              unbalanced_end.pop()
    432              post_delete.insert(0, pre_delete.pop())
    433          else:
    434              # Found a tag that doesn't match
    435              break
    436
    437 -class token(_unicode):
    438      """ Represents a diffable token, generally a word that is displayed to
    439      the user.  Opening tags are attached to this token when they are
    440      adjacent (pre_tags) and closing tags that follow the word
    441      (post_tags).  Some exceptions occur when there are empty tags
    442      adjacent to a word, so there may be close tags in pre_tags, or
    443      open tags in post_tags.
    444
    445      We also keep track of whether the word was originally followed by
    446      whitespace, even though we do not want to treat the word as
    447      equivalent to a similar word that does not have a trailing
    448      space."""
    449
    450      # When this is true, the token will be eliminated from the
    451      # displayed diff if no change has occurred:
    452      hide_when_equal = False
    453
    454 -    def __new__(cls, text, pre_tags=None, post_tags=None, trailing_whitespace=""):
    455          obj = _unicode.__new__(cls, text)
    456
    457          if pre_tags is not None:
    458              obj.pre_tags = pre_tags
    459          else:
    460              obj.pre_tags = []
    461
    462          if post_tags is not None:
    463              obj.post_tags = post_tags
    464          else:
    465              obj.post_tags = []
    466
    467          obj.trailing_whitespace = trailing_whitespace
    468
    469          return obj
    470
    471 -    def __repr__(self):
    472          return 'token(%s, %r, %r, %r)' % (_unicode.__repr__(self), self.pre_tags,
    473                                            self.post_tags, self.trailing_whitespace)
    474
    475 -    def html(self):
    476          return _unicode(self)
    477
    478 -class tag_token(token):
    479
    480      """ Represents a token that is actually a tag.  Currently this is just
    481      the <img> tag, which takes up visible space just like a word but
    482      is only represented in a document by a tag.  """
    483
    484 -    def __new__(cls, tag, data, html_repr, pre_tags=None,
    485                  post_tags=None, trailing_whitespace=""):
    486          obj = token.__new__(cls, "%s: %s" % (type, data),
    487                              pre_tags=pre_tags,
    488                              post_tags=post_tags,
    489                              trailing_whitespace=trailing_whitespace)
    490          obj.tag = tag
    491          obj.data = data
    492          obj.html_repr = html_repr
    493          return obj
    494
    495 -    def __repr__(self):
    496          return 'tag_token(%s, %s, html_repr=%s, post_tags=%r, pre_tags=%r, trailing_whitespace=%r)' % (
    497              self.tag,
    498              self.data,
    499              self.html_repr,
    500              self.pre_tags,
    501              self.post_tags,
    502              self.trailing_whitespace)
    503 -    def html(self):
    504          return self.html_repr
    505
    506 -class href_token(token):
    507
    508      """ Represents the href in an anchor tag.  Unlike other words, we only
    509      show the href when it changes.  """
    510
    511      hide_when_equal = True
    512
    513 -    def html(self):
    514          return ' Link: %s' % self
    515
    516 -def tokenize(html, include_hrefs=True):
    517      """
    518      Parse the given HTML and returns token objects (words with attached tags).
    519
    520      This parses only the content of a page; anything in the head is
    521      ignored, and the <head> and <body> elements are themselves
    522      optional.  The content is then parsed by lxml, which ensures the
    523      validity of the resulting parsed document (though lxml may make
    524      incorrect guesses when the markup is particular bad).
    525
    526      <ins> and <del> tags are also eliminated from the document, as
    527      that gets confusing.
    528
    529      If include_hrefs is true, then the href attribute of <a> tags is
    530      included as a special kind of diffable token."""
    531      if etree.iselement(html):
    532          body_el = html
    533      else:
    534          body_el = parse_html(html, cleanup=True)
    535      # Then we split the document into text chunks for each tag, word, and end tag:
    536      chunks = flatten_el(body_el, skip_tag=True, include_hrefs=include_hrefs)
    537      # Finally re-joining them into token objects:
    538      return fixup_chunks(chunks)
    539
    540 -def parse_html(html, cleanup=True):
    541      """
    542      Parses an HTML fragment, returning an lxml element.  Note that the HTML will be
    543      wrapped in a <div> tag that was not in the original document.
    544
    545      If cleanup is true, make sure there's no <head> or <body>, and get
    546      rid of any <ins> and <del> tags.
    547      """
    548      if cleanup:
    549          # This removes any extra markup or structure like <head>:
    550          html = cleanup_html(html)
    551      return fragment_fromstring(html, create_parent=True)
    552
    553  _body_re = re.compile(r'<body.*?>', re.I|re.S)
    554  _end_body_re = re.compile(r'</body.*?>', re.I|re.S)
    555  _ins_del_re = re.compile(r'</?(ins|del).*?>', re.I|re.S)
    556
    557 -def cleanup_html(html):
    558      """ This 'cleans' the HTML, meaning that any page structure is removed
    559      (only the contents of <body> are used, if there is any <body).
    560      Also <ins> and <del> tags are removed.  """
    561      match = _body_re.search(html)
    562      if match:
    563          html = html[match.end():]
    564      match = _end_body_re.search(html)
    565      if match:
    566          html = html[:match.start()]
    567      html = _ins_del_re.sub('', html)
    568      return html
    569
    570
    571  end_whitespace_re = re.compile(r'[ \t\n\r]$')
    572
    573 -def split_trailing_whitespace(word):
    574      """
    575      This function takes a word, such as 'test\n\n' and returns ('test','\n\n')
    576      """
    577      stripped_length = len(word.rstrip())
    578      return word[0:stripped_length], word[stripped_length:]
    579
    580
    581 -def fixup_chunks(chunks):
    582      """
    583      This function takes a list of chunks and produces a list of tokens.
    584      """
    585      tag_accum = []
    586      cur_word = None
    587      result = []
    588      for chunk in chunks:
    589          if isinstance(chunk, tuple):
    590              if chunk[0] == 'img':
    591                  src = chunk[1]
    592                  tag, trailing_whitespace = split_trailing_whitespace(chunk[2])
    593                  cur_word = tag_token('img', src, html_repr=tag,
    594                                       pre_tags=tag_accum,
    595                                       trailing_whitespace=trailing_whitespace)
    596                  tag_accum = []
    597                  result.append(cur_word)
    598
    599              elif chunk[0] == 'href':
    600                  href = chunk[1]
    601                  cur_word = href_token(href, pre_tags=tag_accum, trailing_whitespace=" ")
    602                  tag_accum = []
    603                  result.append(cur_word)
    604              continue
    605
    606          if is_word(chunk):
    607              chunk, trailing_whitespace = split_trailing_whitespace(chunk)
    608              cur_word = token(chunk, pre_tags=tag_accum, trailing_whitespace=trailing_whitespace)
    609              tag_accum = []
    610              result.append(cur_word)
    611
    612          elif is_start_tag(chunk):
    613              tag_accum.append(chunk)
    614
    615          elif is_end_tag(chunk):
    616              if tag_accum:
    617                  tag_accum.append(chunk)
    618              else:
    619                  assert cur_word, (
    620                      "Weird state, cur_word=%r, result=%r, chunks=%r of %r"
    621                      % (cur_word, result, chunk, chunks))
    622                  cur_word.post_tags.append(chunk)
    623          else:
    624              assert(0)
    625
    626      if not result:
    627          return [token('', pre_tags=tag_accum)]
    628      else:
    629          result[-1].post_tags.extend(tag_accum)
    630
    631      return result
    632
    633
    634  # All the tags in HTML that don't require end tags:
    635  empty_tags = (
    636      'param', 'img', 'area', 'br', 'basefont', 'input',
    637      'base', 'meta', 'link', 'col')
    638
    639  block_level_tags = (
    640      'address',
    641      'blockquote',
    642      'center',
    643      'dir',
    644      'div',
    645      'dl',
    646      'fieldset',
    647      'form',
    648      'h1',
    649      'h2',
    650      'h3',
    651      'h4',
    652      'h5',
    653      'h6',
    654      'hr',
    655      'isindex',
    656      'menu',
    657      'noframes',
    658      'noscript',
    659      'ol',
    660      'p',
    661      'pre',
    662      'table',
    663      'ul',
    664      )
    665
    666  block_level_container_tags = (
    667      'dd',
    668      'dt',
    669      'frameset',
    670      'li',
    671      'tbody',
    672      'td',
    673      'tfoot',
    674      'th',
    675      'thead',
    676      'tr',
    677      )
    678
    679
    680 -def flatten_el(el, include_hrefs, skip_tag=False):
    681      """ Takes an lxml element el, and generates all the text chunks for
    682      that tag.  Each start tag is a chunk, each word is a chunk, and each
    683      end tag is a chunk.
    684
    685      If skip_tag is true, then the outermost container tag is
    686      not returned (just its contents)."""
    687      if not skip_tag:
    688          if el.tag == 'img':
    689              yield ('img', el.get('src'), start_tag(el))
    690          else:
    691              yield start_tag(el)
    692      if el.tag in empty_tags and not el.text and not len(el) and not el.tail:
    693          return
    694      start_words = split_words(el.text)
    695      for word in start_words:
    696          yield html_escape(word)
    697      for child in el:
    698          for item in flatten_el(child, include_hrefs=include_hrefs):
    699              yield item
    700      if el.tag == 'a' and el.get('href') and include_hrefs:
    701          yield ('href', el.get('href'))
    702      if not skip_tag:
    703          yield end_tag(el)
    704          end_words = split_words(el.tail)
    705          for word in end_words:
    706              yield html_escape(word)
    707
    708  split_words_re = re.compile(r'\S+(?:\s+|$)', re.U)
    709
    710 -def split_words(text):
    711      """ Splits some text into words. Includes trailing whitespace
    712      on each word when appropriate.  """
    713      if not text or not text.strip():
    714          return []
    715
    716      words = split_words_re.findall(text)
    717      return words
    718
    719  start_whitespace_re = re.compile(r'^[ \t\n\r]')
    720
    721 -def start_tag(el):
    722      """
    723      The text representation of the start tag for a tag.
    724      """
    725      return '<%s%s>' % (
    726          el.tag, ''.join([' %s="%s"' % (name, html_escape(value, True))
    727                           for name, value in el.attrib.items()]))
    728
    729 -def end_tag(el):
    730      """ The text representation of an end tag for a tag.  Includes
    731      trailing whitespace when appropriate.  """
    732      if el.tail and start_whitespace_re.search(el.tail):
    733          extra = ' '
    734      else:
    735          extra = ''
    736      return '</%s>%s' % (el.tag, extra)
    737
    738 -def is_word(tok):
    739      return not tok.startswith('<')
    740
    741 -def is_end_tag(tok):
    742      return tok.startswith('</')
    743
    744 -def is_start_tag(tok):
    745      return tok.startswith('<') and not tok.startswith('</')
    746
    747 -def fixup_ins_del_tags(html):
    748      """ Given an html string, move any <ins> or <del> tags inside of any
    749      block-level elements, e.g. transform <ins><p>word</p></ins> to
    750      <p><ins>word</ins></p> """
    751      doc = parse_html(html, cleanup=False)
    752      _fixup_ins_del_tags(doc)
    753      html = serialize_html_fragment(doc, skip_outer=True)
    754      return html
    755
    756 -def serialize_html_fragment(el, skip_outer=False):
    757      """ Serialize a single lxml element as HTML.  The serialized form
    758      includes the elements tail.
    759
    760      If skip_outer is true, then don't serialize the outermost tag
    761      """
    762      assert not isinstance(el, basestring), (
    763          "You should pass in an element, not a string like %r" % el)
    764      html = etree.tostring(el, method="html", encoding=_unicode)
    765      if skip_outer:
    766          # Get rid of the extra starting tag:
    767          html = html[html.find('>')+1:]
    768          # Get rid of the extra end tag:
    769          html = html[:html.rfind('<')]
    770          return html.strip()
    771      else:
    772          return html
    773
    774 -def _fixup_ins_del_tags(doc):
    775      """fixup_ins_del_tags that works on an lxml document in-place
    776      """
    777      for tag in ['ins', 'del']:
    778          for el in doc.xpath('descendant-or-self::%s' % tag):
    779              if not _contains_block_level_tag(el):
    780                  continue
    781              _move_el_inside_block(el, tag=tag)
    782              el.drop_tag()
    783              #_merge_element_contents(el)
    784
    785 -def _contains_block_level_tag(el):
    786      """True if the element contains any block-level elements, like <p>, <td>, etc.
    787      """
    788      if el.tag in block_level_tags or el.tag in block_level_container_tags:
    789          return True
    790      for child in el:
    791          if _contains_block_level_tag(child):
    792              return True
    793      return False
    794
    795 -def _move_el_inside_block(el, tag):
    796      """ helper for _fixup_ins_del_tags; actually takes the <ins> etc tags
    797      and moves them inside any block-level tags.  """
    798      for child in el:
    799          if _contains_block_level_tag(child):
    800              break
    801      else:
    802          import sys
    803          # No block-level tags in any child
    804          children_tag = etree.Element(tag)
    805          children_tag.text = el.text
    806          el.text = None
    807          children_tag.extend(list(el))
    808          el[:] = [children_tag]
    809          return
    810      for child in list(el):
    811          if _contains_block_level_tag(child):
    812              _move_el_inside_block(child, tag)
    813              if child.tail:
    814                  tail_tag = etree.Element(tag)
    815                  tail_tag.text = child.tail
    816                  child.tail = None
    817                  el.insert(el.index(child)+1, tail_tag)
    818          else:
    819              child_tag = etree.Element(tag)
    820              el.replace(child, child_tag)
    821              child_tag.append(child)
    822      if el.text:
    823          text_tag = etree.Element(tag)
    824          text_tag.text = el.text
    825          el.text = None
    826          el.insert(0, text_tag)
    827
    828 -def _merge_element_contents(el):
    829      """
    830      Removes an element, but merges its contents into its place, e.g.,
    831      given <p>Hi <i>there!</i></p>, if you remove the <i> element you get
    832      <p>Hi there!</p>
    833      """
    834      parent = el.getparent()
    835      text = el.text or ''
    836      if el.tail:
    837          if not len(el):
    838              text += el.tail
    839          else:
    840              if el[-1].tail:
    841                  el[-1].tail += el.tail
    842              else:
    843                  el[-1].tail = el.tail
    844      index = parent.index(el)
    845      if text:
    846          if index == 0:
    847              previous = None
    848          else:
    849              previous = parent[index-1]
    850          if previous is None:
    851              if parent.text:
    852                  parent.text += text
    853              else:
    854                  parent.text = text
    855          else:
    856              if previous.tail:
    857                  previous.tail += text
    858              else:
    859                  previous.tail = text
    860      parent[index:index+1] = el.getchildren()
    861
    862 -class InsensitiveSequenceMatcher(difflib.SequenceMatcher):
    863      """
    864      Acts like SequenceMatcher, but tries not to find very small equal
    865      blocks amidst large spans of changes
    866      """
    867
    868      threshold = 2
    869
    870 -    def get_matching_blocks(self):
    871          size = min(len(self.b), len(self.b))
    872          threshold = min(self.threshold, size / 4)
    873          actual = difflib.SequenceMatcher.get_matching_blocks(self)
    874          return [item for item in actual
    875                  if item[2] > threshold
    876                  or not item[2]]
    877
    878  if __name__ == '__main__':
    879      from lxml.html import _diffcommand
    880      _diffcommand.main()
    881