Support for async/await
in our own Implementation¶
So what’s necessary for supporting async/await
in our implementation?
Just a single line needs to be added:
Future v5¶
from enum import Enum
from typing import Any, Callable, Generator
from loop import Loop
class CancelledError(Exception):
"""
Raised if a Future is cancelled
"""
class FutureState(Enum):
PENDING = "pending"
DONE = "done"
CANCELLED = "cancelled"
class Future:
"""Return a result in the future v5"""
_result = None
def __init__(self, name: str = None):
self._name = name
self._callbacks = []
self._state = FutureState.PENDING
self._loop = Loop.get_current_loop()
def set_result(self, result: Any):
if self._state != FutureState.PENDING:
raise RuntimeError("Invalid Future state")
self._result = result
self._state = FutureState.DONE
self._schedule_callbacks()
def cancel(self) -> bool:
if self._state != FutureState.PENDING:
return False
self._state = FutureState.CANCELLED
self._schedule_callbacks()
return True
def result(self) -> Any:
if self._state == FutureState.CANCELLED:
raise CancelledError()
if self._state != FutureState.DONE:
raise RuntimeError("Invalid Future state")
return self._result
def done(self) -> bool:
return self._state == FutureState.DONE
def cancelled(self) -> bool:
return self._state == FutureState.CANCELLED
def add_done_callback(self, fn: Callable[["Future"], None]) -> None:
if self._state != FutureState.PENDING:
# we already have a result or are cancelled
self._loop.schedule(self._name, fn, self)
else:
self._callbacks.append(fn)
def _schedule_callbacks(self) -> None:
if not self._callbacks:
return
callbacks = self._callbacks.copy()
self._callbacks.clear()
for callback in callbacks:
self._loop.schedule(self._name, callback, self)
def __repr__(self) -> str:
return (
f"<{self.__class__.__name__} name='{self._name}' "
f"state={self._state} id='{hex(id(self))}'>"
)
def __iter__(self) -> Generator["Future", None, Any]:
yield self
return self.result()
__await__ = __iter__
Future v5¶
--- future4.py 2022-11-09 12:22:03.254019054 +0100
+++ future5.py 2022-11-16 12:18:52.499094129 +0100
@@ -17,7 +17,7 @@
class Future:
- """Return a result in the future v4"""
+ """Return a result in the future v5"""
_result = None
@@ -82,3 +82,5 @@
def __iter__(self) -> Generator["Future", None, Any]:
yield self # some new magic
return self.result()
+
+ __await__ = __iter__
from future import Future
from loop import Loop
from task import Task
async def some_result(result):
future = Future("Some Result")
future.set_result(result)
return await future
async def add(coroutine1, coroutine2):
task1 = Task(coroutine1, "Add X")
task2 = Task(coroutine2, "Add Y")
x = await task1
y = await task2
return x + y
async def main():
return await add(some_result(1), some_result(2))
loop = Loop.get_current_loop()
result = loop.run(main())
print("Loop finished with result", result)
Output:
Loop step 1 [<Handle name='Initial Task' callback='step'>]
Loop step 2 [<Handle name='Add X' callback='step'>, <Handle name='Add Y' callback='step'>]
Loop step 3 [<Handle name='Some Result' callback='_wakeup'>, <Handle name='Some Result' callback='_wakeup'>]
Loop step 4 [<Handle name='Add X' callback='step'>, <Handle name='Add Y' callback='step'>]
Loop step 5 [<Handle name='Add X' callback='_wakeup'>]
Loop step 6 [<Handle name='Initial Task' callback='step'>]
Loop step 7 [<Handle name='Add Y' callback='_wakeup'>]
Loop step 8 [<Handle name='Initial Task' callback='step'>]
Loop step 9 [<Handle name='Initial Task' callback='_done'>]
Loop finished with result 3