Reveal the true shape of type vars
Python's typing system is weak and lacks features well known in other languages.
For example, templating in C++ allows you to instantiate a new object of the templated class T via T(..) which is not possible in Python.
The Silberstral package provides remedy with a simple utility to obtain the actual type that a generic type var refers to:
template<typename T>
class DefaultContainer {
T get(int idx) {
defaultElement = T(); // <- in C++, we can access the actual class of T
...
}
}_T = TypeVar('_T')
class DefaultContainer(Generic[_T]):
def get(self, idx: int) -> _T:
default_element = _T() # <- DOES NOT WORK
...from silberstral import reveal_type_var
_T = TypeVar('_T')
class DefaultList(Generic[_T]):
def get(self, idx: int) -> _T:
T_cls = reveal_type_var(self, _T) # <- Reveals the actual class of _T, e.g., int, str, ...
default_element = T_cls()
...The package is available at pypi:
pip install silberstral
reveal_type_var(obj_or_cls, type_var): Finds the actual type that type_var was instantiated to in obj_or_cls.
Example:
from typing import TypeVar, Generic
from silberstral import reveal_type_var
_T = TypeVar('_T')
class List(Generic[_T]):
pass
reveal_type_var(List[int], _T)
>>> int
str_list = List[str]()
reveal_type_var(str_list, _T)
>>> strreveal_type_vars(obj_or_cls): Lists all type vars and their corresponding instantiations of obj_or_cls
Example:
from typing import TypeVar, Generic
from silberstral import reveal_type_vars
_K = TypeVar('_K')
_V = TypeVar('_V')
class Dict(Generic[_K, _V]):
pass
reveal_type_vars(Dict[int, str])
>>> {_K: int, _V: str}is_type_var_instantiated(obj_or_cls, type_var): Checks whether type_var was instantiated with an actual class in obj_or_cls
Example:
from typing import TypeVar, Generic
from silberstral import is_type_var_instantiated
_T = TypeVar('_T')
class List(Generic[_T]):
pass
is_type_var_instantiated(List, _T)
>>> False
is_type_var_instantiated(List[int], _T)
>>> True
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