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add stub for contextvars.pyi #1968

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JelleZijlstra merged 2 commits into from
Mar 21, 2018
Merged

add stub for contextvars.pyi #1968

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add stub for contextvars.pyi
JelleZijlstra Mar 18, 2018
f77d747
default is not required
JelleZijlstra Mar 21, 2018
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27 changes: 27 additions & 0 deletions stdlib/3.7/contextvars.pyi
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@@ -0,0 +1,27 @@
from typing import Any, Callable, ClassVar, Generic, Mapping, TypeVar, Union

_T = TypeVar('_T')

class ContextVar(Generic[_T]):
def __init__(self, name: str, *, default: _T) -> None: ...
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@1st1 1st1 Mar 21, 2018 •
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default is not a required parameter. It's not typing.Optional either, as it is either of type _T or not passed at all (None is not a valid value).

A couple of examples:

# valid:
int_var: ContextVar[int] = ContextVar(default=1)
int_var: ContextVar[int] = ContextVar()

# invalid:
int_var: ContextVar[int] = ContextVar(default=None)

and

# valid:
int_var: ContextVar[Optional[int]] = ContextVar(default=1)
int_var: ContextVar[Optional[int]] = ContextVar(default=None)
int_var: ContextVar[Optional[int]] = ContextVar()

Here's a pure Python implementaion of PEP 567 / ContextVar: https://github.com/MagicStack/contextvars/blob/master/contextvars/__init__.py#L111

I'm not sure how to express this in terms of typing. Maybe

class ContextVar(Generic[_T]):
    def __init__(self, name: str, *, default: _T=...) -> None: ...

?

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@JelleZijlstra JelleZijlstra Mar 21, 2018

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We can write *, default: _T = .... Sorry for missing this.

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@gvanrossum gvanrossum Mar 21, 2018

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Jelle: If = ... doesn't work, you can use an overload (once without, once with default).

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@1st1 1st1 Mar 21, 2018

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NP!

@property
def name(self) -> str: ...
def get(self, default: _T = ...) -> _T: ...
def set(self, value: _T) -> Token[_T]: ...
def reset(self, token: Token[_T]) -> None: ...

class Token(Generic[_T]):
@property
def var(self) -> ContextVar[_T]: ...
@property
def old_value(self) -> Any: ... # returns either _T or MISSING, but that's hard to express
MISSING: ClassVar[object]

def copy_context() -> Context: ...

# It doesn't make sense to make this generic, because for most Contexts each ContextVar will have
# a different value.
class Context(Mapping[ContextVar[Any], Any]):
def __init__(self) -> None: ...
def run(self, callable: Callable[..., _T], *args: Any, **kwargs: Any) -> _T: ...
def copy(self) -> Context: ...