Yahya Uddin Yahya Uddin - 3 years ago 124
Python Question

How to specify multiple return types using type-hints

I have a function in python that can either return a

bool
or a
list
. Is there a way to specify the return types using type hints.

For example, Is this the correct way to do it?

def foo(id) -> list or bool:
...

Answer Source

From the documentation

class typing.Union

Union type; Union[X, Y] means either X or Y.

Hence the proper way to represent more than one return data type is

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

But do note that typing is not enforced. Python continues to remain a dynamically-typed language. The annotation syntax has been developed to help during the development of the code prior to being released into production. As PEP 484 states, "no type checking happens at runtime."

>>> def foo(a:str) -> list:
...     return("Works")
... 
>>> foo(1)
'Works'

As you can see I am passing a int value and returning a str. However the __annotations__ will be set to the respective values.

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

Please Go through PEP 483 for more about Type hints. Also see What are Type hints in Python 3.5?

Kindly note that this is available only for Python 3.5 and upwards. This is mentioned clearly in PEP 484.

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