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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_collection(self, collection, database_name=None, username=None, password=None):
 """ Get a pymongo collection handle. :param collection: Name of collection :param database_name: (optional) Name of database :param username: (optional) Username to login with :param password: (optional) Password to login with :return: Pymongo collection object """

        _db = self.get_database(database_name, username, password)
        return _db[collection]