def __init__(self, handler):
self.handler = handler<EOL>self.parser = ElementTree.XMLParser(target = ParserTarget(handler))<EOL>self.lock = threading.RLock()<EOL>self.in_use = False<EOL>self._started = False<EOL>
Initialize the reader.

        :Parameters:
            - `handler`: Object to handle stream start, end and stanzas.
        :Types:
            - `handler`: `XMLStreamHandler`