The sgmllib module, shown in Example 5-5, provides a basic SGML parser. It works pretty much the same
as the xmllib
parser, but is less restrictive (and less complete).
Like in xmllib, this parser calls
methods in itself to deal with things like start tags, data sections,
end tags, and entities. If you’re only interested in a few tags, you
can define special start and
end methods.
Example 5-5. Using the sgmllib Module to Extract the Title Element
File: sgmllib-example-1.py
import sgmllib
import string
class FoundTitle(Exception):
pass
class ExtractTitle(sgmllib.SGMLParser):
def _ _init_ _(self, verbose=0):
sgmllib.SGMLParser._ _init_ _(self, verbose)
self.title = self.data = None
def handle_data(self, data):
if self.data is not None:
self.data.append(data)
def start_title(self, attrs):
self.data = []
def end_title(self):
self.title = string.join(self.data, "")
raise FoundTitle # abort parsing!
def extract(file):
# extract title from an HTML/SGML stream
p = ExtractTitle()
try:
while 1:
# read small chunks
s = file.read(512)
if not s:
break
p.feed(s)
p.close()
except FoundTitle:
return p.title
return None
#
# try it out
print "html", "=>", extract(open("samples/sample.htm"))
print "sgml", "=>", extract(open("samples/sample.sgm"))
html => A Title.
sgml => QuotationsTo handle all tags, overload the unknown_starttag
and unknown_endtag methods instead, as Example 5-6 demonstrates.
Example 5-6. Using the sgmllib Module to Format an SGML Document
File: sgmllib-example-2.py
import sgmllib
import cgi, sys
class PrettyPrinter(sgmllib.SGMLParser):
# A simple SGML pretty printer
def _ _init_ _(self):
# initialize base class
sgmllib.SGMLParser._ _init_ _(self)
self.flag = 0
def newline(self):
# force newline, if necessary
if self.flag:
sys.stdout.write("
")
self.flag = 0
def unknown_starttag(self, tag, attrs):
# called for each start tag
# the attrs argument is a list of (attr, value)
# tuples. convert it to a string.
text = ""
for attr, value in attrs:
text = text + " %s='%s'" % (attr, cgi.escape(value))
self.newline()
sys.stdout.write("<%s%s>
" % (tag, text))
def handle_data(self, text):
# called for each text section
sys.stdout.write(text)
self.flag = (text[-1:] != "
")
def handle_entityref(self, text):
# called for each entity
sys.stdout.write("&%s;" % text)
def unknown_endtag(self, tag):
# called for each end tag
self.newline()
sys.stdout.write("<%s>" % tag)
#
# try it out
file = open("samples/sample.sgm")
p = PrettyPrinter()
p.feed(file.read())
p.close()
<chapter>
<title>
Quotations
<title>
<epigraph>
<attribution>
eff-bot, June 1997
<attribution>
<para>
<quote>
Nobody expects the Spanish Inquisition! Amongst
our weaponry are such diverse elements as fear, surprise,
ruthless efficiency, and an almost fanatical devotion to
Guido, and nice red uniforms — oh, damn!
<quote>
<para>
<epigraph>
<chapter>Example 5-7 checks if an SGML document is “well-formed”, in the XML sense. In a well-formed document, all elements are properly nested, with one end tag for each start tag.
To check this, we simply keep a list of open tags, and check that each end tag closes a matching start tag and that there are no open tags when we reach the end of the document.
Example 5-7. Using the sgmllib Module to Check Well-Formedness
File: sgmllib-example-3.py
import sgmllib
class WellFormednessChecker(sgmllib.SGMLParser):
# check that an SGML document is 'well-formed'
# (in the XML sense).
def _ _init_ _(self, file=None):
sgmllib.SGMLParser._ _init_ _(self)
self.tags = []
if file:
self.load(file)
def load(self, file):
while 1:
s = file.read(8192)
if not s:
break
self.feed(s)
self.close()
def close(self):
sgmllib.SGMLParser.close(self)
if self.tags:
raise SyntaxError, "start tag %s not closed" % self.tags[-1]
def unknown_starttag(self, start, attrs):
self.tags.append(start)
def unknown_endtag(self, end):
start = self.tags.pop()
if end != start:
raise SyntaxError, "end tag %s does't match start tag %s" %
(end, start)
try:
c = WellFormednessChecker()
c.load(open("samples/sample.htm"))
except SyntaxError:
raise # report error
else:
print "document is well-formed"
Traceback (innermost last):
...
SyntaxError: end tag head does't match start tag metaFinally, Example 5-8 shows a class that allows you to filter HTML and SGML
documents. To use this class, create your own base class, and
implement the start and end
methods.
Example 5-8. Using the sgmllib Module to Filter SGML Documents
File: sgmllib-example-4.py
import sgmllib
import cgi, string, sys
class SGMLFilter(sgmllib.SGMLParser):
# sgml filter. override start/end to manipulate
# document elements
def _ _init_ _(self, outfile=None, infile=None):
sgmllib.SGMLParser._ _init_ _(self)
if not outfile:
outfile = sys.stdout
self.write = outfile.write
if infile:
self.load(infile)
def load(self, file):
while 1:
s = file.read(8192)
if not s:
break
self.feed(s)
self.close()
def handle_entityref(self, name):
self.write("&%s;" % name)
def handle_data(self, data):
self.write(cgi.escape(data))
def unknown_starttag(self, tag, attrs):
tag, attrs = self.start(tag, attrs)
if tag:
if not attrs:
self.write("<%s>" % tag)
else:
self.write("<%s" % tag)
for k, v in attrs:
self.write(" %s=%s" % (k, repr(v)))
self.write(">")
def unknown_endtag(self, tag):
tag = self.end(tag)
if tag:
self.write("</%s>" % tag)
def start(self, tag, attrs):
return tag, attrs # override
def end(self, tag):
return tag # override
class Filter(SGMLFilter):
def fixtag(self, tag):
if tag == "em":
tag = "i"
if tag == "string":
tag = "b"
return string.upper(tag)
def start(self, tag, attrs):
return self.fixtag(tag), attrs
def end(self, tag):
return self.fixtag(tag)
c = Filter()
c.load(open("samples/sample.htm"))