Package lxml :: Package html :: Module clean

[hide private]
[frames] | no frames]

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