/Python/system/HTMLParser.py

"""A parser for HTML and XHTML."""



# This file is based on sgmllib.py, but the API is slightly different.



# XXX There should be a way to distinguish between PCDATA (parsed

# character data -- the normal case), RCDATA (replaceable character

# data -- only char and entity references and end tags are special)

# and CDATA (character data -- only end tags are special).





import markupbase

import re



# Regular expressions used for parsing



interesting_normal = re.compile('[&<]')

interesting_cdata = re.compile(r'<(/|\Z)')

incomplete = re.compile('&[a-zA-Z#]')



entityref = re.compile('&([a-zA-Z][-.a-zA-Z0-9]*)[^a-zA-Z0-9]')

charref = re.compile('&#(?:[0-9]+|[xX][0-9a-fA-F]+)[^0-9a-fA-F]')



starttagopen = re.compile('<[a-zA-Z]')

piclose = re.compile('>')

commentclose = re.compile(r'--\s*>')

tagfind = re.compile('[a-zA-Z][-.a-zA-Z0-9:_]*')

attrfind = re.compile(

    r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'

    r'(\'[^\']*\'|"[^"]*"|[-a-zA-Z0-9./,:;+*%?!&$\(\)_#=~]*))?')



locatestarttagend = re.compile(r"""

  <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name

  (?:\s+                             # whitespace before attribute name

    (?:[a-zA-Z_][-.:a-zA-Z0-9_]*     # attribute name

      (?:\s*=\s*                     # value indicator

        (?:'[^']*'                   # LITA-enclosed value

          |\"[^\"]*\"                # LIT-enclosed value

          |[^'\">\s]+                # bare value

         )

       )?

     )

   )*

  \s*                                # trailing whitespace

""", re.VERBOSE)

endendtag = re.compile('>')

endtagfind = re.compile('</\s*([a-zA-Z][-.a-zA-Z0-9:_]*)\s*>')





class HTMLParseError(Exception):

    """Exception raised for all parse errors."""



    def __init__(self, msg, position=(None, None)):

        assert msg

        self.msg = msg

        self.lineno = position[0]

        self.offset = position[1]



    def __str__(self):

        result = self.msg

        if self.lineno is not None:

            result = result + ", at line %d" % self.lineno

        if self.offset is not None:

            result = result + ", column %d" % (self.offset + 1)

        return result





class HTMLParser(markupbase.ParserBase):

    """Find tags and other markup and call handler functions.



    Usage:

        p = HTMLParser()

        p.feed(data)

        ...

        p.close()



    Start tags are handled by calling self.handle_starttag() or

    self.handle_startendtag(); end tags by self.handle_endtag().  The

    data between tags is passed from the parser to the derived class

    by calling self.handle_data() with the data as argument (the data

    may be split up in arbitrary chunks).  Entity references are

    passed by calling self.handle_entityref() with the entity

    reference as the argument.  Numeric character references are

    passed to self.handle_charref() with the string containing the

    reference as the argument.

    """



    CDATA_CONTENT_ELEMENTS = ("script", "style")





    def __init__(self):

        """Initialize and reset this instance."""

        self.reset()



    def reset(self):

        """Reset this instance.  Loses all unprocessed data."""

        self.rawdata = ''

        self.lasttag = '???'

        self.interesting = interesting_normal

        markupbase.ParserBase.reset(self)



    def feed(self, data):

        """Feed data to the parser.



        Call this as often as you want, with as little or as much text

        as you want (may include '\n').

        """

        self.rawdata = self.rawdata + data

        self.goahead(0)



    def close(self):

        """Handle any buffered data."""

        self.goahead(1)



    def error(self, message):

        raise HTMLParseError(message, self.getpos())



    __starttag_text = None



    def get_starttag_text(self):

        """Return full source of start tag: '<...>'."""

        return self.__starttag_text



    def set_cdata_mode(self):

        self.interesting = interesting_cdata



    def clear_cdata_mode(self):

        self.interesting = interesting_normal



    # Internal -- handle data as far as reasonable.  May leave state

    # and data to be processed by a subsequent call.  If 'end' is

    # true, force handling all data as if followed by EOF marker.

    def goahead(self, end):

        rawdata = self.rawdata

        i = 0

        n = len(rawdata)

        while i < n:

            match = self.interesting.search(rawdata, i) # < or &

            if match:

                j = match.start()

            else:

                j = n

            if i < j: self.handle_data(rawdata[i:j])

            i = self.updatepos(i, j)

            if i == n: break

            startswith = rawdata.startswith

            if startswith('<', i):

                if starttagopen.match(rawdata, i): # < + letter

                    k = self.parse_starttag(i)

                elif startswith("</", i):

                    k = self.parse_endtag(i)

                elif startswith("<!--", i):

                    k = self.parse_comment(i)

                elif startswith("<?", i):

                    k = self.parse_pi(i)

                elif startswith("<!", i):

                    k = self.parse_declaration(i)

                elif (i + 1) < n:

                    self.handle_data("<")

                    k = i + 1

                else:

                    break

                if k < 0:

                    if end:

                        self.error("EOF in middle of construct")

                    break

                i = self.updatepos(i, k)

            elif startswith("&#", i):

                match = charref.match(rawdata, i)

                if match:

                    name = match.group()[2:-1]

                    self.handle_charref(name)

                    k = match.end()

                    if not startswith(';', k-1):

                        k = k - 1

                    i = self.updatepos(i, k)

                    continue

                else:

                    break

            elif startswith('&', i):

                match = entityref.match(rawdata, i)

                if match:

                    name = match.group(1)

                    self.handle_entityref(name)

                    k = match.end()

                    if not startswith(';', k-1):

                        k = k - 1

                    i = self.updatepos(i, k)

                    continue

                match = incomplete.match(rawdata, i)

                if match:

                    # match.group() will contain at least 2 chars

                    if end and match.group() == rawdata[i:]:

                        self.error("EOF in middle of entity or char ref")

                    # incomplete

                    break

                elif (i + 1) < n:

                    # not the end of the buffer, and can't be confused

                    # with some other construct

                    self.handle_data("&")

                    i = self.updatepos(i, i + 1)

                else:

                    break

            else:

                assert 0, "interesting.search() lied"

        # end while

        if end and i < n:

            self.handle_data(rawdata[i:n])

            i = self.updatepos(i, n)

        self.rawdata = rawdata[i:]



    # Internal -- parse comment, return end or -1 if not terminated

    def parse_comment(self, i, report=1):

        rawdata = self.rawdata

        assert rawdata[i:i+4] == '<!--', 'unexpected call to parse_comment()'

        match = commentclose.search(rawdata, i+4)

        if not match:

            return -1

        if report:

            j = match.start()

            self.handle_comment(rawdata[i+4: j])

        j = match.end()

        return j



    # Internal -- parse processing instr, return end or -1 if not terminated

    def parse_pi(self, i):

        rawdata = self.rawdata

        assert rawdata[i:i+2] == '<?', 'unexpected call to parse_pi()'

        match = piclose.search(rawdata, i+2) # >

        if not match:

            return -1

        j = match.start()

        self.handle_pi(rawdata[i+2: j])

        j = match.end()

        return j



    # Internal -- handle starttag, return end or -1 if not terminated

    def parse_starttag(self, i):

        self.__starttag_text = None

        endpos = self.check_for_whole_start_tag(i)

        if endpos < 0:

            return endpos

        rawdata = self.rawdata

        self.__starttag_text = rawdata[i:endpos]



        # Now parse the data between i+1 and j into a tag and attrs

        attrs = []

        match = tagfind.match(rawdata, i+1)

        assert match, 'unexpected call to parse_starttag()'

        k = match.end()

        self.lasttag = tag = rawdata[i+1:k].lower()



        while k < endpos:

            m = attrfind.match(rawdata, k)

            if not m:

                break

            attrname, rest, attrvalue = m.group(1, 2, 3)

            if not rest:

                attrvalue = None

            elif attrvalue[:1] == '\'' == attrvalue[-1:] or \

                 attrvalue[:1] == '"' == attrvalue[-1:]:

                attrvalue = attrvalue[1:-1]

                attrvalue = self.unescape(attrvalue)

            attrs.append((attrname.lower(), attrvalue))

            k = m.end()



        end = rawdata[k:endpos].strip()

        if end not in (">", "/>"):

            lineno, offset = self.getpos()

            if "\n" in self.__starttag_text:

                lineno = lineno + self.__starttag_text.count("\n")

                offset = len(self.__starttag_text) \

                         - self.__starttag_text.rfind("\n")

            else:

                offset = offset + len(self.__starttag_text)

            self.error("junk characters in start tag: %s"

                       % `rawdata[k:endpos][:20]`)

        if end.endswith('/>'):

            # XHTML-style empty tag: <span attr="value" />

            self.handle_startendtag(tag, attrs)

        else:

            self.handle_starttag(tag, attrs)

            if tag in self.CDATA_CONTENT_ELEMENTS:

                self.set_cdata_mode()

        return endpos



    # Internal -- check to see if we have a complete starttag; return end

    # or -1 if incomplete.

    def check_for_whole_start_tag(self, i):

        rawdata = self.rawdata

        m = locatestarttagend.match(rawdata, i)

        if m:

            j = m.end()

            next = rawdata[j:j+1]

            if next == ">":

                return j + 1

            if next == "/":

                if rawdata.startswith("/>", j):

                    return j + 2

                if rawdata.startswith("/", j):

                    # buffer boundary

                    return -1

                # else bogus input

                self.updatepos(i, j + 1)

                self.error("malformed empty start tag")

            if next == "":

                # end of input

                return -1

            if next in ("abcdefghijklmnopqrstuvwxyz=/"

                        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"):

                # end of input in or before attribute value, or we have the

                # '/' from a '/>' ending

                return -1

            self.updatepos(i, j)

            self.error("malformed start tag")

        raise AssertionError("we should not get here!")



    # Internal -- parse endtag, return end or -1 if incomplete

    def parse_endtag(self, i):

        rawdata = self.rawdata

        assert rawdata[i:i+2] == "</", "unexpected call to parse_endtag"

        match = endendtag.search(rawdata, i+1) # >

        if not match:

            return -1

        j = match.end()

        match = endtagfind.match(rawdata, i) # </ + tag + >

        if not match:

            self.error("bad end tag: %s" % `rawdata[i:j]`)

        tag = match.group(1)

        self.handle_endtag(tag.lower())

        self.clear_cdata_mode()

        return j



    # Overridable -- finish processing of start+end tag: <tag.../>

    def handle_startendtag(self, tag, attrs):

        self.handle_starttag(tag, attrs)

        self.handle_endtag(tag)



    # Overridable -- handle start tag

    def handle_starttag(self, tag, attrs):

        pass



    # Overridable -- handle end tag

    def handle_endtag(self, tag):

        pass



    # Overridable -- handle character reference

    def handle_charref(self, name):

        pass



    # Overridable -- handle entity reference

    def handle_entityref(self, name):

        pass



    # Overridable -- handle data

    def handle_data(self, data):

        pass



    # Overridable -- handle comment

    def handle_comment(self, data):

        pass



    # Overridable -- handle declaration

    def handle_decl(self, decl):

        pass



    # Overridable -- handle processing instruction

    def handle_pi(self, data):

        pass



    def unknown_decl(self, data):

        self.error("unknown declaration: " + `data`)



    # Internal -- helper to remove special character quoting

    def unescape(self, s):

        if '&' not in s:

            return s

        s = s.replace("&lt;", "<")

        s = s.replace("&gt;", ">")

        s = s.replace("&apos;", "'")

        s = s.replace("&quot;", '"')

        s = s.replace("&amp;", "&") # Must be last

        return s