python-generics 0.0.4

A package to determine the values of generic classes through instances or subclasses

Python-Generics

This package provides functionalities to determine the values of generic type variables in Python. As of now, it only supports two functions: get_type_vars and get_filled_type. These functions work also with pydantic generic models (only tested with pydantic > v2.3.0).

The package has no dependencies itself.

Installation

The package is available on PyPI:

pip install python-generics

How to use (in your own application)

The get_type_vars function returns a tuple of all type variables for a given generic type. The TypeVars are determined by Generic if the type is a subclass of Generic. Otherwise, they are determined by the indexed supertypes (the order of the returned tuple is the lexicographical in the list of the supertypes).

from typing import Generic, TypeVar
from generics import get_type_vars

T = TypeVar("T")
U = TypeVar("U")
V = TypeVar("V")

class A(Generic[T, U]):
    pass

class B(A[T, U], Generic[U, T]):
    pass

class C(B[T, U], A[T, V]):
    pass

assert get_type_vars(A) == (T, U)
assert get_type_vars(B) == (U, T)
assert get_type_vars(C) == (T, U, V)

The get_filled_type function determines for a single TypeVar the value if defined somewhere. To determine the value, you have to pass a type or an instance of a type that is a subclass of a generic type of which you want to determine the value of the TypeVar.

Instead of supplying the TypeVar itself, you can define the integer position of the TypeVar in the tuple of TypeVars of the generic type.

from typing import Generic, TypeVar
from generics import get_filled_type

T = TypeVar("T")
U = TypeVar("U")
V = TypeVar("V")

class A(Generic[T, U]):
    pass

class B(A[str, U]):
    pass

assert get_filled_type(A[str, U], A, T) == str
assert get_filled_type(B[int](), A, 0) == str

The get_filled_type function is especially useful if you have generic super types in which you want to determine the value of a TypeVar inside methods.

from typing import Generic, TypeVar, Any
from generics import get_filled_type

T = TypeVar("T")

class MySuperType(Generic[T]):
    def get_type(self) -> Any:
        return get_filled_type(self, MySuperType, 0)

class MySubType(MySuperType[str]):
    pass

assert MySubType().get_type() == str

How to use this Repository on Your Machine (as a developer)

Follow the instructions in our Python template repository.

Contribute

You are very welcome to contribute to this template repository by opening a pull request against the main branch.