Package lxml :: Package html :: Module clean |
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# Source Code for Module lxml.html.clean

      1  """A cleanup tool for HTML.
      2
      3  Removes unwanted tags and content.  See the `Cleaner` class for
      4  details.
      5  """
      6
      7  import re
      8  import copy
      9  try:
     10      from urlparse import urlsplit
     11  except ImportError:
     12      # Python 3
     13      from urllib.parse import urlsplit
     14  from lxml import etree
     15  from lxml.html import defs
     16  from lxml.html import fromstring, XHTML_NAMESPACE
     17  from lxml.html import xhtml_to_html, _transform_result
     18
     19  try:
     20      unichr
     21  except NameError:
     22      # Python 3
     23      unichr = chr
     24  try:
     25      unicode
     26  except NameError:
     27      # Python 3
     28      unicode = str
     29  try:
     30      bytes
     31  except NameError:
     32      # Python < 2.6
     33      bytes = str
     34  try:
     35      basestring
     36  except NameError:
     37      basestring = (str, bytes)
     38
     39
     40  __all__ = ['clean_html', 'clean', 'Cleaner', 'autolink', 'autolink_html',
     41             'word_break', 'word_break_html']
     42
     43  # Look at http://code.sixapart.com/trac/livejournal/browser/trunk/cgi-bin/cleanhtml.pl
     44  #   Particularly the CSS cleaning; most of the tag cleaning is integrated now
     45  # I have multiple kinds of schemes searched; but should schemes be
     46  #   whitelisted instead?
     47  # max height?
     48  # remove images?  Also in CSS?  background attribute?
     49  # Some way to whitelist object, iframe, etc (e.g., if you want to
     50  #   allow *just* embedded YouTube movies)
     51  # Log what was deleted and why?
     52  # style="behavior: ..." might be bad in IE?
     53  # Should we have something for just <meta http-equiv>?  That's the worst of the
     54  #   metas.
     55  # UTF-7 detections?  Example:
     56  #     <HEAD><META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=UTF-7"> </HEAD>+ADw-SCRIPT+AD4-alert('XSS');+ADw-/SCRIPT+AD4-
     57  #   you don't always have to have the charset set, if the page has no charset
     58  #   and there's UTF7-like code in it.
     59  # Look at these tests: http://htmlpurifier.org/live/smoketests/xssAttacks.php
     60
     61
     62  # This is an IE-specific construct you can have in a stylesheet to
     63  # run some Javascript:
     64  _css_javascript_re = re.compile(
     65      r'expression\s*\(.*?\)', re.S|re.I)
     66
     67  # Do I have to worry about @\nimport?
     68  _css_import_re = re.compile(
     69      r'@\s*import', re.I)
     70
     71  # All kinds of schemes besides just javascript: that can cause
     72  # execution:
     73  _is_image_dataurl = re.compile(
     74      r'^data:image/.+;base64', re.I).search
     75  _is_possibly_malicious_scheme = re.compile(
     76      r'(?:javascript|jscript|livescript|vbscript|data|about|mocha):',
     77      re.I).search
     78 -def _is_javascript_scheme(s):
     79      if _is_image_dataurl(s):
     80          return None
     81      return _is_possibly_malicious_scheme(s)
     82
     83  _substitute_whitespace = re.compile(r'[\s\x00-\x08\x0B\x0C\x0E-\x19]+').sub
     84  # FIXME: should data: be blocked?
     85
     86  # FIXME: check against: http://msdn2.microsoft.com/en-us/library/ms537512.aspx
     87  _conditional_comment_re = re.compile(
     88      r'\[if[\s\n\r]+.*?][\s\n\r]*>', re.I|re.S)
     89
     90  _find_styled_elements = etree.XPath(
     91      "descendant-or-self::*[@style]")
     92
     93  _find_external_links = etree.XPath(
     94      ("descendant-or-self::a  [normalize-space(@href) and substring(normalize-space(@href),1,1) != '#'] |"
     95       "descendant-or-self::x:a[normalize-space(@href) and substring(normalize-space(@href),1,1) != '#']"),
     96      namespaces={'x':XHTML_NAMESPACE})
     97
     98
     99 -class Cleaner(object):
    100      """
    101      Instances cleans the document of each of the possible offending
    102      elements.  The cleaning is controlled by attributes; you can
    103      override attributes in a subclass, or set them in the constructor.
    104
    105      ``scripts``:
    106          Removes any ``<script>`` tags.
    107
    108      ``javascript``:
    109          Removes any Javascript, like an ``onclick`` attribute. Also removes stylesheets
    110          as they could contain Javascript.
    111
    112      ``comments``:
    113          Removes any comments.
    114
    115      ``style``:
    116          Removes any style tags.
    117
    118      ``inline_style``
    119          Removes any style attributes.  Defaults to the value of the ``style`` option.
    120
    121      ``links``:
    122          Removes any ``<link>`` tags
    123
    124      ``meta``:
    125          Removes any ``<meta>`` tags
    126
    127      ``page_structure``:
    128          Structural parts of a page: ``<head>``, ``<html>``, ``<title>``.
    129
    130      ``processing_instructions``:
    131          Removes any processing instructions.
    132
    133      ``embedded``:
    134          Removes any embedded objects (flash, iframes)
    135
    136      ``frames``:
    137          Removes any frame-related tags
    138
    139      ``forms``:
    140          Removes any form tags
    141
    142      ``annoying_tags``:
    143          Tags that aren't *wrong*, but are annoying.  ``<blink>`` and ``<marquee>``
    144
    145      ``remove_tags``:
    146          A list of tags to remove.  Only the tags will be removed,
    147          their content will get pulled up into the parent tag.
    148
    149      ``kill_tags``:
    150          A list of tags to kill.  Killing also removes the tag's content,
    151          i.e. the whole subtree, not just the tag itself.
    152
    153      ``allow_tags``:
    154          A list of tags to include (default include all).
    155
    156      ``remove_unknown_tags``:
    157          Remove any tags that aren't standard parts of HTML.
    158
    159      ``safe_attrs_only``:
    160          If true, only include 'safe' attributes (specifically the list
    161          from the feedparser HTML sanitisation web site).
    162
    163      ``safe_attrs``:
    164          A set of attribute names to override the default list of attributes
    165          considered 'safe' (when safe_attrs_only=True).
    166
    167      ``add_nofollow``:
    168          If true, then any <a> tags will have ``rel="nofollow"`` added to them.
    169
    170      ``host_whitelist``:
    171          A list or set of hosts that you can use for embedded content
    172          (for content like ``<object>``, ``<link rel="stylesheet">``, etc).
    173          You can also implement/override the method
    174          ``allow_embedded_url(el, url)`` or ``allow_element(el)`` to
    175          implement more complex rules for what can be embedded.
    176          Anything that passes this test will be shown, regardless of
    177          the value of (for instance) ``embedded``.
    178
    179          Note that this parameter might not work as intended if you do not
    180          make the links absolute before doing the cleaning.
    181
    182          Note that you may also need to set ``whitelist_tags``.
    183
    184      ``whitelist_tags``:
    185          A set of tags that can be included with ``host_whitelist``.
    186          The default is ``iframe`` and ``embed``; you may wish to
    187          include other tags like ``script``, or you may want to
    188          implement ``allow_embedded_url`` for more control.  Set to None to
    189          include all tags.
    190
    191      This modifies the document *in place*.
    192      """
    193
    194      scripts = True
    195      javascript = True
    196      comments = True
    197      style = False
    198      inline_style = None
    199      links = True
    200      meta = True
    201      page_structure = True
    202      processing_instructions = True
    203      embedded = True
    204      frames = True
    205      forms = True
    206      annoying_tags = True
    207      remove_tags = None
    208      allow_tags = None
    209      kill_tags = None
    210      remove_unknown_tags = True
    211      safe_attrs_only = True
    212      safe_attrs = defs.safe_attrs
    213      add_nofollow = False
    214      host_whitelist = ()
    215      whitelist_tags = set(['iframe', 'embed'])
    216
    217 -    def __init__(self, **kw):
    218          for name, value in kw.items():
    219              if not hasattr(self, name):
    220                  raise TypeError(
    221                      "Unknown parameter: %s=%r" % (name, value))
    222              setattr(self, name, value)
    223          if self.inline_style is None and 'inline_style' not in kw:
    224              self.inline_style = self.style
    225
    226      # Used to lookup the primary URL for a given tag that is up for
    227      # removal:
    228      _tag_link_attrs = dict(
    229          script='src',
    230          link='href',
    231          # From: http://java.sun.com/j2se/1.4.2/docs/guide/misc/applet.html
    232          # From what I can tell, both attributes can contain a link:
    233          applet=['code', 'object'],
    234          iframe='src',
    235          embed='src',
    236          layer='src',
    237          # FIXME: there doesn't really seem like a general way to figure out what
    238          # links an <object> tag uses; links often go in <param> tags with values
    239          # that we don't really know.  You'd have to have knowledge about specific
    240          # kinds of plugins (probably keyed off classid), and match against those.
    241          ##object=?,
    242          # FIXME: not looking at the action currently, because it is more complex
    243          # than than -- if you keep the form, you should keep the form controls.
    244          ##form='action',
    245          a='href',
    246          )
    247
    248 -    def __call__(self, doc):
    249          """
    250          Cleans the document.
    251          """
    252          if hasattr(doc, 'getroot'):
    253              # ElementTree instance, instead of an element
    254              doc = doc.getroot()
    255          # convert XHTML to HTML
    256          xhtml_to_html(doc)
    257          # Normalize a case that IE treats <image> like <img>, and that
    258          # can confuse either this step or later steps.
    259          for el in doc.iter('image'):
    260              el.tag = 'img'
    261          if not self.comments:
    262              # Of course, if we were going to kill comments anyway, we don't
    263              # need to worry about this
    264              self.kill_conditional_comments(doc)
    265
    266          kill_tags = set(self.kill_tags or ())
    267          remove_tags = set(self.remove_tags or ())
    268          allow_tags = set(self.allow_tags or ())
    269
    270          if self.scripts:
    271              kill_tags.add('script')
    272          if self.safe_attrs_only:
    273              safe_attrs = set(self.safe_attrs)
    274              for el in doc.iter(etree.Element):
    275                  attrib = el.attrib
    276                  for aname in attrib.keys():
    277                      if aname not in safe_attrs:
    278                          del attrib[aname]
    279          if self.javascript:
    280              if not (self.safe_attrs_only and
    281                      self.safe_attrs == defs.safe_attrs):
    282                  # safe_attrs handles events attributes itself
    283                  for el in doc.iter(etree.Element):
    284                      attrib = el.attrib
    285                      for aname in attrib.keys():
    286                          if aname.startswith('on'):
    287                              del attrib[aname]
    288              doc.rewrite_links(self._remove_javascript_link,
    289                                resolve_base_href=False)
    290              # If we're deleting style then we don't have to remove JS links
    291              # from styles, otherwise...
    292              if not self.inline_style:
    293                  for el in _find_styled_elements(doc):
    294                      old = el.get('style')
    295                      new = _css_javascript_re.sub('', old)
    296                      new = _css_import_re.sub('', new)
    297                      if self._has_sneaky_javascript(new):
    298                          # Something tricky is going on...
    299                          del el.attrib['style']
    300                      elif new != old:
    301                          el.set('style', new)
    302              if not self.style:
    303                  for el in list(doc.iter('style')):
    304                      if el.get('type', '').lower().strip() == 'text/javascript':
    305                          el.drop_tree()
    306                          continue
    307                      old = el.text or ''
    308                      new = _css_javascript_re.sub('', old)
    309                      # The imported CSS can do anything; we just can't allow:
    310                      new = _css_import_re.sub('', old)
    311                      if self._has_sneaky_javascript(new):
    312                          # Something tricky is going on...
    313                          el.text = '/* deleted */'
    314                      elif new != old:
    315                          el.text = new
    316          if self.comments or self.processing_instructions:
    317              # FIXME: why either?  I feel like there's some obscure reason
    318              # because you can put PIs in comments...?  But I've already
    319              # forgotten it
    320              kill_tags.add(etree.Comment)
    321          if self.processing_instructions:
    322              kill_tags.add(etree.ProcessingInstruction)
    323          if self.style:
    324              kill_tags.add('style')
    325          if self.inline_style:
    326              etree.strip_attributes(doc, 'style')
    327          if self.links:
    328              kill_tags.add('link')
    329          elif self.style or self.javascript:
    330              # We must get rid of included stylesheets if Javascript is not
    331              # allowed, as you can put Javascript in them
    332              for el in list(doc.iter('link')):
    333                  if 'stylesheet' in el.get('rel', '').lower():
    334                      # Note this kills alternate stylesheets as well
    335                      if not self.allow_element(el):
    336                          el.drop_tree()
    337          if self.meta:
    338              kill_tags.add('meta')
    339          if self.page_structure:
    340              remove_tags.update(('head', 'html', 'title'))
    341          if self.embedded:
    342              # FIXME: is <layer> really embedded?
    343              # We should get rid of any <param> tags not inside <applet>;
    344              # These are not really valid anyway.
    345              for el in list(doc.iter('param')):
    346                  found_parent = False
    347                  parent = el.getparent()
    348                  while parent is not None and parent.tag not in ('applet', 'object'):
    349                      parent = parent.getparent()
    350                  if parent is None:
    351                      el.drop_tree()
    352              kill_tags.update(('applet',))
    353              # The alternate contents that are in an iframe are a good fallback:
    354              remove_tags.update(('iframe', 'embed', 'layer', 'object', 'param'))
    355          if self.frames:
    356              # FIXME: ideally we should look at the frame links, but
    357              # generally frames don't mix properly with an HTML
    358              # fragment anyway.
    359              kill_tags.update(defs.frame_tags)
    360          if self.forms:
    361              remove_tags.add('form')
    362              kill_tags.update(('button', 'input', 'select', 'textarea'))
    363          if self.annoying_tags:
    364              remove_tags.update(('blink', 'marquee'))
    365
    366          _remove = []
    367          _kill = []
    368          for el in doc.iter():
    369              if el.tag in kill_tags:
    370                  if self.allow_element(el):
    371                      continue
    372                  _kill.append(el)
    373              elif el.tag in remove_tags:
    374                  if self.allow_element(el):
    375                      continue
    376                  _remove.append(el)
    377
    378          if _remove and _remove[0] == doc:
    379              # We have to drop the parent-most tag, which we can't
    380              # do.  Instead we'll rewrite it:
    381              el = _remove.pop(0)
    382              el.tag = 'div'
    383              el.attrib.clear()
    384          elif _kill and _kill[0] == doc:
    385              # We have to drop the parent-most element, which we can't
    386              # do.  Instead we'll clear it:
    387              el = _kill.pop(0)
    388              if el.tag != 'html':
    389                  el.tag = 'div'
    390              el.clear()
    391
    392          _kill.reverse() # start with innermost tags
    393          for el in _kill:
    394              el.drop_tree()
    395          for el in _remove:
    396              el.drop_tag()
    397
    398          if self.remove_unknown_tags:
    399              if allow_tags:
    400                  raise ValueError(
    401                      "It does not make sense to pass in both allow_tags and remove_unknown_tags")
    402              allow_tags = set(defs.tags)
    403          if allow_tags:
    404              bad = []
    405              for el in doc.iter():
    406                  if el.tag not in allow_tags:
    407                      bad.append(el)
    408              if bad:
    409                  if bad[0] is doc:
    410                      el = bad.pop(0)
    411                      el.tag = 'div'
    412                      el.attrib.clear()
    413                  for el in bad:
    414                      el.drop_tag()
    415          if self.add_nofollow:
    416              for el in _find_external_links(doc):
    417                  if not self.allow_follow(el):
    418                      rel = el.get('rel')
    419                      if rel:
    420                          if ('nofollow' in rel
    421                                  and ' nofollow ' in (' %s ' % rel)):
    422                              continue
    423                          rel = '%s nofollow' % rel
    424                      else:
    425                          rel = 'nofollow'
    426                      el.set('rel', rel)
    427
    428 -    def allow_follow(self, anchor):
    429          """
    430          Override to suppress rel="nofollow" on some anchors.
    431          """
    432          return False
    433
    434 -    def allow_element(self, el):
    435          if el.tag not in self._tag_link_attrs:
    436              return False
    437          attr = self._tag_link_attrs[el.tag]
    438          if isinstance(attr, (list, tuple)):
    439              for one_attr in attr:
    440                  url = el.get(one_attr)
    441                  if not url:
    442                      return False
    443                  if not self.allow_embedded_url(el, url):
    444                      return False
    445              return True
    446          else:
    447              url = el.get(attr)
    448              if not url:
    449                  return False
    450              return self.allow_embedded_url(el, url)
    451
    452 -    def allow_embedded_url(self, el, url):
    453          if (self.whitelist_tags is not None
    454              and el.tag not in self.whitelist_tags):
    455              return False
    456          scheme, netloc, path, query, fragment = urlsplit(url)
    457          netloc = netloc.lower().split(':', 1)[0]
    458          if scheme not in ('http', 'https'):
    459              return False
    460          if netloc in self.host_whitelist:
    461              return True
    462          return False
    463
    464 -    def kill_conditional_comments(self, doc):
    465          """
    466          IE conditional comments basically embed HTML that the parser
    467          doesn't normally see.  We can't allow anything like that, so
    468          we'll kill any comments that could be conditional.
    469          """
    470          bad = []
    471          self._kill_elements(
    472              doc, lambda el: _conditional_comment_re.search(el.text),
    473              etree.Comment)
    474
    475 -    def _kill_elements(self, doc, condition, iterate=None):
    476          bad = []
    477          for el in doc.iter(iterate):
    478              if condition(el):
    479                  bad.append(el)
    480          for el in bad:
    481              el.drop_tree()
    482
    483 -    def _remove_javascript_link(self, link):
    484          # links like "j a v a s c r i p t:" might be interpreted in IE
    485          new = _substitute_whitespace('', link)
    486          if _is_javascript_scheme(new):
    487              # FIXME: should this be None to delete?
    488              return ''
    489          return link
    490
    491      _substitute_comments = re.compile(r'/\*.*?\*/', re.S).sub
    492
    493 -    def _has_sneaky_javascript(self, style):
    494          """
    495          Depending on the browser, stuff like ``e x p r e s s i o n(...)``
    496          can get interpreted, or ``expre/* stuff */ssion(...)``.  This
    497          checks for attempt to do stuff like this.
    498
    499          Typically the response will be to kill the entire style; if you
    500          have just a bit of Javascript in the style another rule will catch
    501          that and remove only the Javascript from the style; this catches
    502          more sneaky attempts.
    503          """
    504          style = self._substitute_comments('', style)
    505          style = style.replace('\\', '')
    506          style = _substitute_whitespace('', style)
    507          style = style.lower()
    508          if 'javascript:' in style:
    509              return True
    510          if 'expression(' in style:
    511              return True
    512          return False
    513
    514 -    def clean_html(self, html):
    515          result_type = type(html)
    516          if isinstance(html, basestring):
    517              doc = fromstring(html)
    518          else:
    519              doc = copy.deepcopy(html)
    520          self(doc)
    521          return _transform_result(result_type, doc)
    522
    523  clean = Cleaner()
    524  clean_html = clean.clean_html
    525
    526  ############################################################
    527  ## Autolinking
    528  ############################################################
    529
    530  _link_regexes = [
    531      re.compile(r'(?P<body>https?://(?P<host>[a-z0-9._-]+)(?:/[/\-_.,a-z0-9%&?;=~]*)?(?:\([/\-_.,a-z0-9%&?;=~]*\))?)', re.I),
    532      # This is conservative, but autolinking can be a bit conservative:
    533      re.compile(r'mailto:(?P<body>[a-z0-9._-]+@(?P<host>[a-z0-9_.-]+[a-z]))', re.I),
    534      ]
    535
    536  _avoid_elements = ['textarea', 'pre', 'code', 'head', 'select', 'a']
    537
    538  _avoid_hosts = [
    539      re.compile(r'^localhost', re.I),
    540      re.compile(r'\bexample\.(?:com|org|net)$', re.I),
    541      re.compile(r'^127\.0\.0\.1$'),
    542      ]
    543
    544  _avoid_classes = ['nolink']
    545
    546 -def autolink(el, link_regexes=_link_regexes,
    547               avoid_elements=_avoid_elements,
    548               avoid_hosts=_avoid_hosts,
    549               avoid_classes=_avoid_classes):
    550      """
    551      Turn any URLs into links.
    552
    553      It will search for links identified by the given regular
    554      expressions (by default mailto and http(s) links).
    555
    556      It won't link text in an element in avoid_elements, or an element
    557      with a class in avoid_classes.  It won't link to anything with a
    558      host that matches one of the regular expressions in avoid_hosts
    559      (default localhost and 127.0.0.1).
    560
    561      If you pass in an element, the element's tail will not be
    562      substituted, only the contents of the element.
    563      """
    564      if el.tag in avoid_elements:
    565          return
    566      class_name = el.get('class')
    567      if class_name:
    568          class_name = class_name.split()
    569          for match_class in avoid_classes:
    570              if match_class in class_name:
    571                  return
    572      for child in list(el):
    573          autolink(child, link_regexes=link_regexes,
    574                   avoid_elements=avoid_elements,
    575                   avoid_hosts=avoid_hosts,
    576                   avoid_classes=avoid_classes)
    577          if child.tail:
    578              text, tail_children = _link_text(
    579                  child.tail, link_regexes, avoid_hosts, factory=el.makeelement)
    580              if tail_children:
    581                  child.tail = text
    582                  index = el.index(child)
    583                  el[index+1:index+1] = tail_children
    584      if el.text:
    585          text, pre_children = _link_text(
    586              el.text, link_regexes, avoid_hosts, factory=el.makeelement)
    587          if pre_children:
    588              el.text = text
    589              el[:0] = pre_children
    590
    591 -def _link_text(text, link_regexes, avoid_hosts, factory):
    592      leading_text = ''
    593      links = []
    594      last_pos = 0
    595      while 1:
    596          best_match, best_pos = None, None
    597          for regex in link_regexes:
    598              regex_pos = last_pos
    599              while 1:
    600                  match = regex.search(text, pos=regex_pos)
    601                  if match is None:
    602                      break
    603                  host = match.group('host')
    604                  for host_regex in avoid_hosts:
    605                      if host_regex.search(host):
    606                          regex_pos = match.end()
    607                          break
    608                  else:
    609                      break
    610              if match is None:
    611                  continue
    612              if best_pos is None or match.start() < best_pos:
    613                  best_match = match
    614                  best_pos = match.start()
    615          if best_match is None:
    616              # No more matches
    617              if links:
    618                  assert not links[-1].tail
    619                  links[-1].tail = text
    620              else:
    621                  assert not leading_text
    622                  leading_text = text
    623              break
    624          link = best_match.group(0)
    625          end = best_match.end()
    626          if link.endswith('.') or link.endswith(','):
    627              # These punctuation marks shouldn't end a link
    628              end -= 1
    629              link = link[:-1]
    630          prev_text = text[:best_match.start()]
    631          if links:
    632              assert not links[-1].tail
    633              links[-1].tail = prev_text
    634          else:
    635              assert not leading_text
    636              leading_text = prev_text
    637          anchor = factory('a')
    638          anchor.set('href', link)
    639          body = best_match.group('body')
    640          if not body:
    641              body = link
    642          if body.endswith('.') or body.endswith(','):
    643              body = body[:-1]
    644          anchor.text = body
    645          links.append(anchor)
    646          text = text[end:]
    647      return leading_text, links
    648
    649 -def autolink_html(html, *args, **kw):
    650      result_type = type(html)
    651      if isinstance(html, basestring):
    652          doc = fromstring(html)
    653      else:
    654          doc = copy.deepcopy(html)
    655      autolink(doc, *args, **kw)
    656      return _transform_result(result_type, doc)
    657
    658  autolink_html.__doc__ = autolink.__doc__
    659
    660  ############################################################
    661  ## Word wrapping
    662  ############################################################
    663
    664  _avoid_word_break_elements = ['pre', 'textarea', 'code']
    665  _avoid_word_break_classes = ['nobreak']
    666
    667 -def word_break(el, max_width=40,
    668                 avoid_elements=_avoid_word_break_elements,
    669                 avoid_classes=_avoid_word_break_classes,
    670                 break_character=unichr(0x200b)):
    671      """
    672      Breaks any long words found in the body of the text (not attributes).
    673
    674      Doesn't effect any of the tags in avoid_elements, by default
    675      ``<textarea>`` and ``<pre>``
    676
    677      Breaks words by inserting &#8203;, which is a unicode character
    678      for Zero Width Space character.  This generally takes up no space
    679      in rendering, but does copy as a space, and in monospace contexts
    680      usually takes up space.
    681
    682      See http://www.cs.tut.fi/~jkorpela/html/nobr.html for a discussion
    683      """
    684      # Character suggestion of &#8203 comes from:
    685      #   http://www.cs.tut.fi/~jkorpela/html/nobr.html
    686      if el.tag in _avoid_word_break_elements:
    687          return
    688      class_name = el.get('class')
    689      if class_name:
    690          dont_break = False
    691          class_name = class_name.split()
    692          for avoid in avoid_classes:
    693              if avoid in class_name:
    694                  dont_break = True
    695                  break
    696          if dont_break:
    697              return
    698      if el.text:
    699          el.text = _break_text(el.text, max_width, break_character)
    700      for child in el:
    701          word_break(child, max_width=max_width,
    702                     avoid_elements=avoid_elements,
    703                     avoid_classes=avoid_classes,
    704                     break_character=break_character)
    705          if child.tail:
    706              child.tail = _break_text(child.tail, max_width, break_character)
    707
    708 -def word_break_html(html, *args, **kw):
    709      result_type = type(html)
    710      doc = fromstring(html)
    711      word_break(doc, *args, **kw)
    712      return _transform_result(result_type, doc)
    713
    714 -def _break_text(text, max_width, break_character):
    715      words = text.split()
    716      for word in words:
    717          if len(word) > max_width:
    718              replacement = _insert_break(word, max_width, break_character)
    719              text = text.replace(word, replacement)
    720      return text
    721
    722  _break_prefer_re = re.compile(r'[^a-z]', re.I)
    723
    724 -def _insert_break(word, width, break_character):
    725      orig_word = word
    726      result = ''
    727      while len(word) > width:
    728          start = word[:width]
    729          breaks = list(_break_prefer_re.finditer(start))
    730          if breaks:
    731              last_break = breaks[-1]
    732              # Only walk back up to 10 characters to find a nice break:
    733              if last_break.end() > width-10:
    734                  # FIXME: should the break character be at the end of the
    735                  # chunk, or the beginning of the next chunk?
    736                  start = word[:last_break.end()]
    737          result += start + break_character
    738          word = word[len(start):]
    739      result += word
    740      return result
    741