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I'm working on a python3 project where we use the typing module type hints throughout.

It seems that we use typing.Dict and typing.Mapping pretty much interchangeably.

Is there a reason to prefer one over the other?

Managed to answer this myself.

typing.Dict should be used to indicate a literal dict type with support for element type hinting i.e. Dict[bytes, str]

typing.Mapping is an object which defines the __getitem__,__len__,__iter__ magic methods

typing.MutableMapping is an object which defines same as Mapping but with __setitem__,__delitem__ magic methods as well.

typing.Mapping et al. are based on the abc types in this table

Rule of a thumb: expect generic types, return specific types. This gives users of your functions and classes the biggest flexibility and safety. – Hubert Grzeskowiak May 22, 2019 at 2:03 One more difference. Dict is invariant, Mapping is covariant. It's important when e.g. you have a function receiving Dict[A,B] and try to pass Dict[A,C] where C is a subtype of B . You will get typing error which can be avoided by using Mapping[A,B] , See realpython.com/python-type-checking/… . – Dmitry Vyal Oct 9, 2020 at 9:10 @HubertGrzeskowiak Besides the rule, if a function preprocess on the inputs, should I use Dict as both input and output types? Receiving a MutableMapping and then returns a Dict seems a bit inconvenient in this case ... – Saddle Point Feb 23, 2022 at 9:55 @HubertGrzeskowiak Hint about generic types is good.. but in this case which is more generic, Mapping or Dict? – hubatish Aug 22, 2022 at 19:18 @hubatish Mapping is more generic because there are more classes than Dict that implement the 3 magic methods that Mapping stands for. – DBedrenko Oct 17, 2022 at 17:43

As suggested by the official python (3.11) documentation typing.Dict is useful for annotating return types. To annotate arguments it is preferred to use an abstract collection type such as Mapping .

Also, typing.Dict has been deprecated since version 3.9. in favor of dict .

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