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Direct instantiation of `typing.Union` in Python


By : Francois
Date : September 17 2020, 02:00 AM
will help you That's not how Union works.
Union is the same thing as the union in C.
code :
def f(a: Union[int, str]) -> None:
   ...


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Preventing a class from direct instantiation in Python


By : Felix
Date : March 29 2020, 07:55 AM
Any of those help I would override __new__() in the base class and simply fail to instantiate at all if it's the base class.
code :
class BaseClass(object):

    def __new__(cls, *args, **kwargs):
        if cls is BaseClass:
            raise TypeError("base class may not be instantiated")
        return object.__new__(cls, *args, **kwargs)

How to cast a typing.Union to one of its subtypes in Python?


By : Tak Hung
Date : March 29 2020, 07:55 AM
Any of those help You'd have to use cast():
code :
process(cast(Foo, d["foo"]), cast(Bar, d["bar"]))
from typing import Dict, Union, NewType, NamedTuple

Foo = NewType("Foo", str)
Bar = NewType("Bar", int)

class FooBarData(NamedTuple):
    foo: Foo
    bar: Bar

def get_data() -> FooBarData:
    return FooBarData(foo=Foo("one"), bar=Bar(2))
d = get_data()
process(d.foo, d.bar)

Python typing Union of class and it's instance


By : hong thu
Date : March 29 2020, 07:55 AM
Hope that helps See typing/issue 266. This has been fixed and no longer appears in updated versions of Python.
With Python 3.6.1, the function is compiled fine and the annotations stored correctly:
code :
>>> def bar(o: Union[Foo, Type[Foo]]):
...     print(1)
>>> typing.get_type_hints(bar)
{'o': typing.Union[__main__.Foo, typing.Type[__main__.Foo]]}

Is Python 3.x dictionary lint type check (typing) set at instantiation


By : user1433343
Date : March 29 2020, 07:55 AM
seems to work fine
updating extending and adding keys does not seem to change the types a dictionary declares
code :
def foo(a: int = 1, b: str = "b") -> None:
    d: Dict[str, Union[int, str]] = {"a": a}
    d.update({"b": b})

    # If you want to check your assumption at runtime
    b_regex = d["b"]
    assert isinstance(b_regex, str)
    print(re.findall(b_regex, "baba"))

    # If you don't want/don't need to check the type
    print(re.findall(cast(str, d["b"]), "baba"))
def foo(a: int = 1, b: str = "b") -> None:
    d: Dict[str, Any] = {"a": a}
    d.update({"b": b})
    print(re.findall(d["b"], "baba"))

Python - typing - union of subscriptable type


By : user2190760
Date : March 29 2020, 07:55 AM
around this issue I'd like to create an Array type which should be subscriptable and be a Union of typing.List and numpy.ndarray types. I know numpy doesn't come with stubs, but those numpy stubs (by Machinalis) should work fine as they are subsriptable. , Creating a type alias of Union[List[T], Array[T]] ought to work:
code :
from typing import TypeVar, Union, List

T = TypeVar('T')
Array = Union[List[T], numpy.ndarray[T]]

def foo(bar: Array[int]) -> None: pass
from __future__ import annotations
from typing import TypeVar, Union, List, TYPE_CHECKING

if TYPE_CHECKING:
    T = TypeVar('T')
    Array = Union[List[T], numpy.ndarray[T]]

def foo(bar: Array[int]) -> None: pass
from typing import TypeVar, Union, List, TYPE_CHECKING

if TYPE_CHECKING:
    T = TypeVar('T')
    Array = Union[List[T], numpy.ndarray[T]]

def foo(bar: "Array[int]") -> None: pass
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