How to specify multiple return types using type-hints

Question

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  - gt  list or bool

User · Answer

Python 3 10  use     Example for a function which takes a single argument that is either an int or str and returns either an int or str  def func arg  int   str  - gt  int   str                                                      type of arg   return type  Python 3 5 - 3 9  use typing Union   from typing import Union def func arg  Union int  str   - gt  Union int  str                                                                      type of arg         return type  For the special case of X   None you can use Optional X

User · Answer

The statement def foo client id  str  - gt  list or bool  when evaluated is equivalent to def foo client id  str  - gt  list  and will therefore not do what you want   The native way to describe a  either A or B  type hint is Union  thanks to Bhargav Rao    def foo client id  str  - gt  Union list  bool     I do not want to be the  Why do you want to do this anyway  guy  but maybe having 2 return types isn t what you want   If you want to return a bool to indicate some type of special error-case  consider using Exceptions instead  If you want to return a bool as some special value  maybe an empty list would be a good representation  You can also indicate that None could be returned with Optional list

User · Answer

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   from typing import Union   def foo client id  str  - gt  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     gt  gt  gt  def foo a str  - gt  list          return  Works         gt  gt  gt  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     gt  gt  gt  foo   annotations      return    lt class  list  gt    a    lt class  str  gt       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

User · Answer

In case anyone landed here in search of  quot how to specify types of multiple return values  quot   use Tuple type value1       type valueN  from typing import Tuple  def f   - gt  Tuple dict  str       a    1  2      b    quot hello quot      return a  b  More info  How to annotate types of multiple return values

[python] How to specify multiple return types using type-hints

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