The xmllib Module

The xmlib module provides a simple XML parser, using regular expressions to pull the XML data apart, as shown in Example 5-1. The parser does basic checks on the document, such as a check to see that there is only one top-level element and a check to see that all tags are balanced.

You feed XML data to this parser piece by piece (as data arrives over a network, for example). The parser calls methods in itself for start tags, data sections, end tags, and entities, among other things.

If you're only interested in a few tags, you can define special start_tag and end_tag methods, where tag is the tag name. The start functions are called with the attributes given as a dictionary.

Example 5-1. Using the xmllib Module to Extract Information from an Element

File: xmllib-example-1.py import xmllib class Parser(xmllib.XMLParser): # get quotation number def _ _init_ _(self, file=None): xmllib.XMLParser._ _init_ _(self) if file: self.load(file) def load(self, file): while 1: s = file.read(512) if not s: break self.feed(s) self.close() def start_quotation(self, attrs): print "id =>", attrs.get("id") raise EOFError try: c = Parser() c.load(open("samples/sample.xml")) except EOFError: pass id => 031

Example 5-2 contains a simple (and incomplete) rendering engine. The parser maintains an element stack (_ _tags), which it passes to the renderer, together with text fragments. The renderer looks up the current tag hierarchy in a style dictionary, and if it isn't already there, it creates a new style descriptor by combining bits and pieces from the stylesheet.

Example 5-2. Using the xmllib Module

File: xmllib-example-2.py import xmllib import string, sys STYLESHEET = { # each element can contribute one or more style elements "quotation": {"style": "italic"}, "lang": {"weight": "bold"}, "name": {"weight": "medium"}, } class Parser(xmllib.XMLParser): # a simple styling engine def _ _init_ _(self, renderer): xmllib.XMLParser._ _init_ _(self) self._ _data = [] self._ _tags = [] self._ _renderer = renderer def load(self, file): while 1: s = file.read(8192) if not s: break self.feed(s) self.close() def handle_data(self, data): self._ _data.append(data) def unknown_starttag(self, tag, attrs): if self._ _data: text = string.join(self._ _data, "") self._ _renderer.text(self._ _tags, text) self._ _tags.append(tag) self._ _data = [] def unknown_endtag(self, tag): self._ _tags.pop() if self._ _data: text = string.join(self._ _data, "") self._ _renderer.text(self._ _tags, text) self._ _data = [] class DumbRenderer: def _ _init_ _(self): self.cache = {} def text(self, tags, text): # render text in the style given by the tag stack tags = tuple(tags) style = self.cache.get(tags) if style is None: # figure out a combined style style = {} for tag in tags: s = STYLESHEET.get(tag) if s: style.update(s) self.cache[tags] = style # update cache # write to standard output sys.stdout.write("%s => " % style) sys.stdout.write(" " + repr(text) + " ") # # try it out r = DumbRenderer() c = Parser(r) c.load(open("samples/sample.xml")) {'style': 'italic'} => 'I've had a lot of developers come up to me and12say, "I haven't had this much fun in a long time. It sure beats12writing ' {'style': 'italic', 'weight': 'bold'} => 'Cobol' {'style': 'italic'} => '" -- ' {'style': 'italic', 'weight': 'medium'} => 'James Gosling' {'style': 'italic'} => ', on12' {'weight': 'bold'} => 'Java' {'style': 'italic'} => '.'