python - pymongo why we can use a dot to get a collection instance? -

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from pymongo import mongoclient dbc = mongoclient("localhost").test.test

just snippet above, can use . instead of get_database("test") , get_collection("test") database instance or collection instance. despite convenience, wonder makes syntactic sugar happen?

there __getattr__() magic method making dot notation/attribute lookup happen.

let's source code. mongoclient class defines __getaattr__ method , instantiates database class name:

def __getattr__(self, name):     """get database name.     raises :class:`~pymongo.errors.invalidname` if invalid     database name used.     :parameters:       - `name`: name of database     """     if name.startswith('_'):         raise attributeerror(             "mongoclient has no attribute %r. access %s"             " database, use client[%r]." % (name, name, name))     return self.__getitem__(name)  def __getitem__(self, name):     """get database name.     raises :class:`~pymongo.errors.invalidname` if invalid     database name used.     :parameters:       - `name`: name of database     """     return database.database(self, name)

and same goes database class.


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