'Return a verbose string representation of the ``ProbabilisticDependencyGrammar``
:rtype: str'

def __str__(self):

    str = (u'Statistical    dependency    grammar    with    %d    productions' % len(self._productions))
    for production in self._productions:
        str += (u'\n        %s' % production)
    str += u'\nEvents:'
    for event in self._events:
        str += (u'\n        %d:%s' % (self._events[event], event))
    str += u'\nTags:'
    for tag_word in self._tags:
        str += (u'\n    %s: DCTB (%s)' % (tag_word, self._tags[tag_word]))
    return str
