Access subtype of type hint

Question

class MyClass:
    prop: list[str]

MyClass.__annotations__
# {'prop': list[str]}

How do I access "str"?

As a more generic question, given an obnoxiously complex and long type hint, like prop: list[set[list[list[str] | set[int]]]], how do I access the internal values programmatically?

https://docs.python.org/3/library/typing.html#typing.get_args — user2357112, Jan 31 '23 at 22:52
Given that Python typing hints have zero impact at runtime, I think you’ll need to clarify what you mean by “access” and what for. — Abhijit Sarkar, Jan 31 '23 at 22:54

score 0 · Accepted Answer · answered Jan 31 '23 at 23:02

Here is a function that will recursively pretty print the type and all the types inside it, using typing.get_args as suggested by @user2357112 :

from typing import List, Set, Union
import typing

complex_type = Union[List[str], Set[int]]

def log_type_layers(typing_type, indent=4, depth=0):
    current_type = typing_type
    print(" "*indent*depth + str(current_type))
    for subtype in typing.get_args(current_type):
        log_type_layers(subtype, indent=indent, depth=depth+1)
        
log_type_layers(complex_type)

Output:

typing.Union[typing.List[str], typing.Set[int]]
    typing.List[str]
        <class 'str'>
    typing.Set[int]
        <class 'int'>

Access subtype of type hint

1 Answers1