This document is a quick cheat sheet showing how the PEP 484 typeannotation notation represents various common types in Python 3.
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Note
Technically many of the type annotations shown below are redundant,because mypy can derive them from the type of the expression. Somany of the examples have a dual purpose: show how to write theannotation, and show the inferred types.
Variables¶
Python 3.6 introduced a syntax for annotating variables in PEP 526and we use it in most examples.
Built-in types¶
Functions¶
Python 3 supports an annotation syntax for function declarations.
When you’re puzzled or when things are complicated¶
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Standard “duck types”¶
In typical Python code, many functions that can take a list or a dictas an argument only need their argument to be somehow “list-like” or“dict-like”. A specific meaning of “list-like” or “dict-like” (orsomething-else-like) is called a “duck type”, and several duck typesthat are common in idiomatic Python are standardized.
You can even make your own duck types using Protocols and structural subtyping.
Classes¶
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Coroutines and asyncio¶
See Typing async/await for the full detail on typing coroutines and asynchronous code.
Miscellaneous¶
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Decorators¶
Decorator functions can be expressed via generics. SeeDeclaring decorators for more details.