def __init__(self, doc_repo):
"""Constructor for `BaseExtension`.
This should never get called directly.
Args:
doc_repo: The `doc_repo.DocRepo` instance which documentation
is being generated.
"""
self.doc_repo = doc_repo
DocTree.resolve_placeholder_signal.connect(
self.__resolve_placeholder_cb)
DocTree.update_signal.connect(self.__update_doc_tree_cb)
if not hasattr(self, 'formatters'):
self.formatters = {"html": HtmlFormatter([])}
self.__created_symbols = defaultdict(OrderedSet)
self.__package_root = None
