Added a tree builder for the built-in HTMLParser, and tests.

1 files changed, 263 insertions, 0 deletions

diff --git a/bs4/builder/__init__.py b/bs4/builder/__init__.py
new file mode 100644
index 0000000..17dcff3
--- /dev/null
+++ b/bs4/builder/__init__.py
@@ -0,0 +1,263 @@
+from collections import defaultdict
+import re
+import sys
+
+__all__ = [
+    'HTMLTreeBuilder',
+    'SAXTreeBuilder',
+    'TreeBuilder',
+    'TreeBuilderRegistry',
+    ]
+
+# Some useful features for a TreeBuilder to have.
+FAST = 'fast'
+PERMISSIVE = 'permissive'
+STRICT = 'strict'
+XML = 'xml'
+HTML = 'html'
+HTML_5 = 'html5'
+
+
+class TreeBuilderRegistry(object):
+
+    def __init__(self):
+        self.builders_for_feature = defaultdict(list)
+        self.builders = []
+
+    def register(self, treebuilder_class):
+        """Register a treebuilder based on its advertised features."""
+        for feature in treebuilder_class.features:
+            self.builders_for_feature[feature].insert(0, treebuilder_class)
+        self.builders.insert(0, treebuilder_class)
+
+    def lookup(self, *features):
+        if len(self.builders) == 0:
+            # There are no builders at all.
+            return None
+
+        if len(features) == 0:
+            # They didn't ask for any features. Give them the most
+            # recently registered builder.
+            return self.builders[0]
+
+        # Go down the list of features in order, and eliminate any builders
+        # that don't match every feature.
+        features = list(features)
+        features.reverse()
+        candidates = None
+        candidate_set = None
+        while len(features) > 0:
+            feature = features.pop()
+            we_have_the_feature = self.builders_for_feature.get(feature, [])
+            if len(we_have_the_feature) > 0:
+                if candidates is None:
+                    candidates = we_have_the_feature
+                    candidate_set = set(candidates)
+                else:
+                    # Eliminate any candidates that don't have this feature.
+                    candidate_set = candidate_set.intersection(
+                        set(we_have_the_feature))
+
+        # The only valid candidates are the ones in candidate_set.
+        # Go through the original list of candidates and pick the first one
+        # that's in candidate_set.
+        if candidate_set is None:
+            return None
+        for candidate in candidates:
+            if candidate in candidate_set:
+                return candidate
+        return None
+
+# The BeautifulSoup class will take feature lists from developers and use them
+# to look up builders in this registry.
+builder_registry = TreeBuilderRegistry()
+
+
+class TreeBuilder(object):
+    """Turn a document into a Beautiful Soup object tree."""
+
+    features = []
+
+    is_xml = False
+    preserve_whitespace_tags = set()
+    empty_element_tags = None # A tag will be considered an empty-element
+                              # tag when and only when it has no contents.
+
+    def __init__(self):
+        self.soup = None
+
+    def reset(self):
+        pass
+
+    def can_be_empty_element(self, tag_name):
+        """Might a tag with this name be an empty-element tag?
+
+        The final markup may or may not actually present this tag as
+        self-closing.
+
+        For instance: an HTMLBuilder does not consider a <p> tag to be
+        an empty-element tag (it's not in
+        HTMLBuilder.empty_element_tags). This means an empty <p> tag
+        will be presented as "<p></p>", not "<p />".
+
+        The default implementation has no opinion about which tags are
+        empty-element tags, so a tag will be presented as an
+        empty-element tag if and only if it has no contents.
+        "<foo></foo>" will become "<foo />", and "<foo>bar</foo>" will
+        be left alone.
+        """
+        if self.empty_element_tags is None:
+            return True
+        return tag_name in self.empty_element_tags
+
+    def feed(self, markup):
+        raise NotImplementedError()
+
+    def prepare_markup(self, markup, user_specified_encoding=None,
+                       document_declared_encoding=None):
+        return markup, None, None
+
+    def test_fragment_to_document(self, fragment):
+        """Wrap an HTML fragment to make it look like a document.
+
+        Different parsers do this differently. For instance, lxml
+        introduces an empty <head> tag, and html5lib
+        doesn't. Abstracting this away lets us write simple tests
+        which run HTML fragments through the parser and compare the
+        results against other HTML fragments.
+
+        This method should not be used outside of tests.
+        """
+        return fragment
+
+    def set_up_substitutions(self, tag):
+        pass
+
+
+class SAXTreeBuilder(TreeBuilder):
+    """A Beautiful Soup treebuilder that listens for SAX events."""
+
+    def feed(self, markup):
+        raise NotImplementedError()
+
+    def close(self):
+        pass
+
+    def startElement(self, name, attrs):
+        attrs = dict((key[1], value) for key, value in attrs.items())
+        #print "Start %s, %r" % (name, attrs)
+        self.soup.handle_starttag(name, attrs)
+
+    def endElement(self, name):
+        #print "End %s" % name
+        self.soup.handle_endtag(name)
+
+    def startElementNS(self, nsTuple, nodeName, attrs):
+        # Throw away (ns, nodeName) for now.
+        self.startElement(nodeName, attrs)
+
+    def endElementNS(self, nsTuple, nodeName):
+        # Throw away (ns, nodeName) for now.
+        self.endElement(nodeName)
+        #handler.endElementNS((ns, node.nodeName), node.nodeName)
+
+    def startPrefixMapping(self, prefix, nodeValue):
+        # Ignore the prefix for now.
+        pass
+
+    def endPrefixMapping(self, prefix):
+        # Ignore the prefix for now.
+        # handler.endPrefixMapping(prefix)
+        pass
+
+    def characters(self, content):
+        self.soup.handle_data(content)
+
+    def startDocument(self):
+        pass
+
+    def endDocument(self):
+        pass
+
+
+class HTMLTreeBuilder(TreeBuilder):
+    """This TreeBuilder knows facts about HTML.
+
+    Such as which tags are empty-element tags.
+    """
+
+    preserve_whitespace_tags = set(['pre', 'textarea'])
+    empty_element_tags = set(['br' , 'hr', 'input', 'img', 'meta',
+                              'spacer', 'link', 'frame', 'base'])
+
+    # Used by set_up_substitutions to detect the charset in a META tag
+    CHARSET_RE = re.compile("((^|;)\s*charset=)([^;]*)", re.M)
+
+    def set_up_substitutions(self, tag):
+        if tag.name != 'meta':
+            return False
+
+        http_equiv = tag.get('http-equiv')
+        content = tag.get('content')
+
+        if (http_equiv is not None
+            and content is not None
+            and http_equiv.lower() == 'content-type'):
+            # This is an interesting meta tag.
+            match = self.CHARSET_RE.search(content)
+            if match:
+                if (self.soup.declared_html_encoding is not None or
+                    self.soup.original_encoding == self.soup.from_encoding):
+                    # An HTML encoding was sniffed while converting
+                    # the document to Unicode, or an HTML encoding was
+                    # sniffed during a previous pass through the
+                    # document, or an encoding was specified
+                    # explicitly and it worked. Rewrite the meta tag.
+                    def rewrite(match):
+                        return match.group(1) + "%SOUP-ENCODING%"
+                    tag['content'] = self.CHARSET_RE.sub(rewrite, content)
+                    return True
+                else:
+                    # This is our first pass through the document.
+                    # Go through it again with the encoding information.
+                    new_charset = match.group(3)
+                    if (new_charset is not None
+                        and new_charset != self.soup.original_encoding):
+                        self.soup.declared_html_encoding = new_charset
+                        self.soup._feed(self.soup.declared_html_encoding)
+                        raise StopParsing
+                    pass
+        return False
+
+
+def register_treebuilders_from(module):
+    """Copy TreeBuilders from the given module into this module."""
+    # I'm fairly sure this is not the best way to do this.
+    this_module = sys.modules[__package__]
+    for name in module.__all__:
+        obj = getattr(module, name)
+
+        if issubclass(obj, TreeBuilder):
+            setattr(this_module, name, obj)
+            this_module.__all__.append(name)
+            # Register the builder while we're at it.
+            this_module.builder_registry.register(obj)
+
+# Builders are registered in reverse order of priority, so that custom
+# builder registrations will take precedence. In general, we want
+# html5lib to take precedence over lxml, because it's more
+# reliable. And we only want to use HTMLParser as a last result.
+import _htmlparser
+register_treebuilders_from(_htmlparser)
+try:
+    import _lxml
+    register_treebuilders_from(_lxml)
+except ImportError:
+    # They don't have lxml installed.
+    pass
+try:
+    import _html5lib
+    register_treebuilders_from(_html5lib)
+except ImportError:
+    # They don't have html5lib installed.
+    pass