The first argument provides the initial value for the
default_factory attribute; it defaults to
All remaining arguments are treated the same as if they were
passed to the dict constructor, including keyword arguments.
New in version 2.5.
defaultdict objects support the following method in addition to the standard dict operations:
None, this raises an KeyError exception with the key as argument.
If default_factory is not
None, it is called without
arguments to provide a default value for the given key, this
value is inserted in the dictionary for the key, and returned.
If calling default_factory raises an exception this exception is propagated unchanged.
This method is called by the __getitem__ method of the dict class when the requested key is not found; whatever it returns or raises is then returned or raised by __getitem__.
defaultdict objects support the following instance variable:
None, if absent.