How Can I Specify Multiple Return Types in Python Using Type Hints?

Combining Return Types in Python Using Type-Hints

In Python, functions can return one of several types. Specifying these return types using type-hints increases code clarity and allows for earlier error detection.

To specify multiple return types, use the | (bitwise OR) operator for Python 3.10 and above:

def foo(client_id: str) -> list | bool:
    ...

Before Python 3.10, use the Union type from the typing module:

from typing import Union

def foo(client_id: str) -> Union[list, bool]:
    ...

Note that type-checking is not enforced during runtime. Type-hints serve as guidelines for code development, providing enhanced clarity and aiding in earlier detection of potential issues. For example, even though foo is annotated with str input and list output, the following code executes successfully, returning a str:

>>> def foo(a: str) -> list:
...     return "Works"
...

>>> foo(1)
'Works'

However, the function's annotation is preserved:

>>> foo.__annotations__
{'return': <class 'list'>, 'a': <class 'str'>}

Refer to PEP 483 for further details on type-hints and PEP 484 for the introduction of | syntax for return types in Python 3.10.

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