def __init__(self, field):
        if isinstance(field, type):
            self.field = field()
        else:
            self.field = field
Given entity primary key as Reference Proto, returns entity kind.
dataset/ETHPy150Open noirbizarre/flask-restplus/flask_restplus/marshalling.py/marshal_with_field.__init__--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/google/appengine/ext/analytics/entity.py/EntityKind