async/await

async_context_managers.py

import asyncio


class CM:

    async def __aenter__(self):
        print(1)
        await asyncio.sleep(0.01)
        print(2)
        return self

    async def __aexit__(self, exc_type, exc_val, exc_tb):
        print(exc_type, exc_val, exc_tb)
        await asyncio.sleep(0.01)

class CM2:

    @asyncio.coroutine
    def __aenter__(self):
        print(1)
        yield from asyncio.sleep(0.01)
        print(2)
        return self

    @asyncio.coroutine
    def __aexit__(self, exc_type, exc_val, exc_tb):
        print(exc_type, exc_val, exc_tb)
        yield from asyncio.sleep(0.01)


async def f():
    cm = CM()
    async with cm as c:
        assert cm is c
        await asyncio.sleep(0.01)
        raise RuntimeError('a bug')

    print('done')


async def f2():
    cm = CM()
    async with cm as c:
        assert cm is c
        await asyncio.sleep(0.01)
        raise RuntimeError('a bug')

    print('done')

loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(f())
except RuntimeError as exc:
    print(exc)
try:
    loop.run_until_complete(f2())
except RuntimeError as exc:
    print(exc)
loop.close()

async_func_waiting_future.py

import asyncio


async def f(fut):
    val = await fut
    return val

loop = asyncio.get_event_loop()
fut = asyncio.Future(loop=loop)
loop.call_soon(fut.set_result, 123)
ret = loop.run_until_complete(f(fut))
loop.close()
print(ret)

stream_client.py

import asyncio

END = b'Bye-bye!\n'

async def echo_client():
    reader, writer = await asyncio.open_connection('localhost', 8000)
    writer.write(b'Hello, world\n')
    writer.write(b'What a fine day it is.\n')
    writer.write(END)
    while True:
        line = await reader.readline()
        print('received:', line)
        if line == END or not line:
            break
    writer.close()

loop = asyncio.get_event_loop()
loop.run_until_complete(echo_client())
loop.close()

stream_server.py

import asyncio

async def echo_server():
    await asyncio.start_server(handle_connection, 'localhost', 8000)

async def handle_connection(reader, writer):
    while True:
        data = await reader.read(8192)
        if not data:
            break
        writer.write(data)

loop = asyncio.get_event_loop()
loop.run_until_complete(echo_server())
try:
    loop.run_forever()
finally:
    loop.close()