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* origin/main: (67 commits) Move `Token`, `TokenKind` and `Tokens` to `ruff-python-ast` (#21760) [ty] Don't confuse multiple occurrences of `typing.Self` when binding bound methods (#21754) Use our org-wide Renovate preset (#21759) Delete `my-script.py` (#21751) [ty] Move `all_members`, and related types/routines, out of `ide_support.rs` (#21695) [ty] Fix find-references for import aliases (#21736) [ty] add tests for workspaces (#21741) [ty] Stop testing the (brittle) constraint set display implementation (#21743) [ty] Use generator over list comprehension to avoid cast (#21748) [ty] Add a diagnostic for prohibited `NamedTuple` attribute overrides (#21717) [ty] Fix subtyping with `type[T]` and unions (#21740) Use `npm ci --ignore-scripts` everywhere (#21742) [`flake8-simplify`] Fix truthiness assumption for non-iterable arguments in tuple/list/set calls (`SIM222`, `SIM223`) (#21479) [`flake8-use-pathlib`] Mark fixes unsafe for return type changes (`PTH104`, `PTH105`, `PTH109`, `PTH115`) (#21440) [ty] Fix auto-import code action to handle pre-existing import Enable PEP 740 attestations when publishing to PyPI (#21735) [ty] Fix find references for type defined in stub (#21732) Use OIDC instead of codspeed token (#21719) [ty] Exclude `typing_extensions` from completions unless it's really available [ty] Fix false positives for `class F(Generic[*Ts]): ...` (#21723) ...
120 lines
2.2 KiB
Markdown
120 lines
2.2 KiB
Markdown
# `async` / `await`
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## Basic
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```py
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async def retrieve() -> int:
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return 42
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async def main():
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result = await retrieve()
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reveal_type(result) # revealed: int
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```
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## Generic `async` functions
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```py
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from typing import TypeVar
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T = TypeVar("T")
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async def persist(x: T) -> T:
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return x
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async def f(x: int):
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result = await persist(x)
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reveal_type(result) # revealed: int
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```
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## Use cases
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### `Future`
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```py
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import asyncio
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import concurrent.futures
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def blocking_function() -> int:
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return 42
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async def main():
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loop = asyncio.get_event_loop()
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with concurrent.futures.ThreadPoolExecutor() as pool:
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result = await loop.run_in_executor(pool, blocking_function)
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reveal_type(result) # revealed: int
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```
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### `asyncio.Task`
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```py
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import asyncio
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async def f() -> int:
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return 1
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async def main():
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task = asyncio.create_task(f())
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result = await task
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reveal_type(result) # revealed: int
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```
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### `asyncio.gather`
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```py
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import asyncio
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async def task(name: str) -> int:
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return len(name)
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async def main():
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(a, b) = await asyncio.gather(
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task("A"),
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task("B"),
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)
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reveal_type(a) # revealed: int
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reveal_type(b) # revealed: int
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```
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## Under the hood
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```toml
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[environment]
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python-version = "3.12" # Use 3.12 to be able to use PEP 695 generics
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```
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Let's look at the example from the beginning again:
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```py
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async def retrieve() -> int:
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return 42
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```
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When we look at the signature of this function, we see that it actually returns a `CoroutineType`:
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```py
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reveal_type(retrieve) # revealed: def retrieve() -> CoroutineType[Any, Any, int]
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```
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The expression `await retrieve()` desugars into a call to the `__await__` dunder method on the
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`CoroutineType` object, followed by a `yield from`. Let's first see the return type of `__await__`:
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```py
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reveal_type(retrieve().__await__()) # revealed: Generator[Any, None, int]
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```
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We can see that this returns a `Generator` that yields `Any`, and eventually returns `int`. For the
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final type of the `await` expression, we retrieve that third argument of the `Generator` type:
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```py
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from typing import Generator
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def _():
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result = yield from retrieve().__await__()
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reveal_type(result) # revealed: int
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```
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