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