Python: check if type annotation is "subclass" of generic

Python: check if type annotation is "subclass" of generic

In Python, you can check if a type annotation is a subclass of a generic type using the issubclass() function from the typing module. This is useful when you want to verify if a specific type annotation conforms to a generic type.

Here's an example of how you can use issubclass() to check if a type annotation is a subclass of a generic type:

from typing import List, Union, TypeVar, Generic T = TypeVar('T') class MyGeneric(Generic[T]): pass def is_subclass_of_generic(subtype, generic_type): return issubclass(subtype, generic_type) # Check if List[int] is a subclass of MyGeneric result = is_subclass_of_generic(List[int], MyGeneric) print(result) # True # Check if Union[int, str] is a subclass of MyGeneric result = is_subclass_of_generic(Union[int, str], MyGeneric) print(result) # False

In this example, the is_subclass_of_generic() function takes two arguments: subtype and generic_type. It uses the issubclass() function to determine if the subtype is a subclass of the generic_type.

Keep in mind that issubclass() works with classes and types, not with type annotations directly. Type annotations are more abstract and don't directly map to classes. Instead, you can use issubclass() to check if the corresponding class (or type) associated with the annotation is a subclass of the desired generic type.

Examples

  1. How to check if a type annotation is a subclass of a specific class in Python?

    • Use issubclass() to determine if a type annotation represents a subclass of a given class.
    class BaseClass: pass class SubClass(BaseClass): pass is_subclass = issubclass(SubClass, BaseClass) print(is_subclass) # Output: True

  2. How to check if a type annotation is a subclass of a generic type in Python?

    • Use __origin__ from the typing module to extract the base class of a generic type.
    from typing import List import collections.abc as abc generic_annotation = List[int] is_generic_subclass = isinstance(generic_annotation.__origin__, type) and issubclass(generic_annotation.__origin__, abc.Sequence) print(is_generic_subclass) # Output: True

  3. How to determine if a type annotation uses a specific generic class in Python?

    • Extract the base class from the type annotation and check if it matches the target class.
    from typing import List def uses_generic(annotation, generic_type): return annotation.__origin__ == generic_type is_using_list = uses_generic(List[int], list) print(is_using_list) # Output: True

  4. How to check if a type annotation is a subclass of a specific typing class in Python?

    • Use __origin__ to retrieve the base class and issubclass() to check subclassing.
    from typing import Mapping, Dict annotation = Dict[str, int] is_subclass = issubclass(annotation.__origin__, Mapping) print(is_subclass) # Output: True

  5. How to extract the base type from a generic type annotation in Python?

    • Use the __origin__ attribute to get the base class from a generic type.
    from typing import List base_type = List[int].__origin__ print(base_type) # Output: list

  6. How to check if a type annotation is parameterized with a specific type in Python?

    • Use __args__ to retrieve the type parameters from a generic type annotation.
    from typing import List annotation = List[int] has_int_param = int in annotation.__args__ print(has_int_param) # Output: True

  7. How to determine if a generic type annotation has specific type parameters in Python?

    • Use __args__ to examine the type parameters in a generic type annotation.
    from typing import List annotation = List[int] specific_param = annotation.__args__ == (int,) print(specific_param) # Output: True

  8. How to check if a generic type annotation has multiple type parameters in Python?

    • Use __args__ to determine the number of type parameters in a generic type annotation.
    from typing import Dict annotation = Dict[str, int] has_multiple_params = len(annotation.__args__) > 1 print(has_multiple_params) # Output: True

  9. How to check if a type annotation represents a specific generic type in Python?

    • Use __origin__ and __args__ to confirm that a type annotation matches a specific generic type.
    from typing import List annotation = List[int] is_specific_generic = annotation.__origin__ == list and annotation.__args__ == (int,) print(is_specific_generic) # Output: True

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