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import urlparse # for AbsoluteUrls
import lxml.html
import lxml.html.builder
class Filter(object):
'''Filters are used during postprocessing of docs generation to modify the
HTML.
They are constructed in a pipeline, where the output of one is fed as input
to the next.'''
def __init__(self, context, root):
self.context = context
self.root = root
def process(self):
'''process can alter the DOM by mutating self.root, an lxml.Element.
Returning a value overrides self.root and passes that value to
subsequent filters.'''
raise NotImplementedError
def pipeline(context, filters, s):
# Assume all files are utf8 encoded.
parser = lxml.html.HTMLParser(encoding='UTF-8')
# A filter takes a single element, but the input may not have a root
# element, it might be a list of elements when parsed. Create a 'dummy'
# parent that wraps the input.
node = lxml.html.fragment_fromstring(s, create_parent='dummy', parser=parser)
if not filters:
return s
for fcls in filters:
f = fcls(context, node)
modified = f.process()
if modified is not None:
dummy = lxml.html.builder.E('dummy')
dummy.append(modified)
node = dummy
# Remove the dummy parent created before.
assert node.tag == 'dummy', 'expected element with tag dummy, got %s' % node.tag
serialized = lxml.html.tostring(node, encoding='UTF-8')
return serialized[len('<dummy>'):-len('</dummy>')]
class AbsoluteUrls(Filter):
'''AbsoluteUrls traverses img and a elements and changes the url they point
to to be absolute to the url they were scraped from.'''
def process(self):
for e in self.root.cssselect('a,img'):
if e.tag == 'img':
attr = 'src'
elif e.tag == 'a':
attr = 'href'
else:
raise ValueError('expected <a> or <img>')
link = e.get(attr)
if link:
absoluteurl = urlparse.urljoin(self.context.current_url,
link)
e.set(attr, absoluteurl)