def __init__(self, searcher, fieldname):
        self.N = searcher.doc_count_all()
        self.collection_total = searcher.field_length(fieldname)
        self.mean_length = self.collection_total / self.N
dataset/ETHPy150Open tallstreet/Whoosh-AppEngine/src/whoosh/classify.py/ExpansionModel.__init__/original