Python协程中的更新函数调用

Question

我有一个简单的类，用于获取URL，同时使用单独线程上的新循环定期更新访问令牌：

import asyncio
import aiohttp
from threading import Thread
from random import randint

LOOP = asyncio.get_event_loop()

NEW_LOOP = asyncio.new_event_loop()
t = Thread(target=NEW_LOOP.run_forever)
t.start()

class SOME_CLASS(object):
    def __init__(self, loop=LOOP, new_loop=NEW_LOOP):
        self.token = None
        self.loop = loop
        self.new_loop = new_loop
        self.semaphore = asyncio.Semaphore(3)
        self.session = aiohttp.ClientSession(loop=self.loop)

        asyncio.run_coroutine_threadsafe(self.get_token(), self.new_loop)

    def _get_headers(self):
        headers = {
                    'x-access-token': str(self.token),
                    'content-type': 'application/json',
                  }

        return headers

    async def get_token(self):
        while True:
            self.token = randint(1, 100)
            await asyncio.sleep(2)        

    async def fetch(self, url):
        async with self.semaphore:
            headers = self._get_headers()
            async with self.session.get(url, headers=headers) as response:
                await response.read()
                return headers

    async def fetch_all(self):
        urls = ['https://httpbin.org/get?x={i}'for i in range(1000)]
        futures = asyncio.as_completed([self.fetch(url) for url in urls])
        for future in futures:
            await asyncio.sleep(1)
            headers = await future
            print(f'headers: {headers}  token: {self.token}')

    def run(self):
        self.loop.run_until_complete(self.fetch_all())

if __name__ == '__main__':
    sc = SOME_CLASS()
    sc.run()

然而，我注意到，即使self.token确实每两秒更新一次，存储在headers中的令牌仍然保持不变。看起来好像self._get_headers()是提前被调用的，而不是在它获得信号量之后：

headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 8
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 8
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 78
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 78
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 41
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 56
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 56
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 74
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 74
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 4
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 4
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 10
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 10
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 44
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 44
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 28
headers: {'x-access-token': '8', 'content-type': 'application/json'}  token: 28

如何确保在发送http请求之前，令牌在headers中得到实际更新？

Answer 1

asyncio.sleep(2)设置得很高，将其设置为0.2，将您的调试打印放入fetch并查看其更新

Answer 2

对于一个基本的Python问题，您有一个复杂的包装器。变量self.token是一个简单的整数。存储在headers字典中的值是这个简单整数的字符串表示。当您将self.token重新赋值给一个不同的整数时，程序将无法知道您希望同时更改哪些其他对象。

一种解决方案是使self.token成为具有内部状态的对象。该对象可以在程序中的不同位置引用。当你改变它的内部状态时，它当然会立即生效。下面是一个带有class Token的小程序来说明这一点。我希望你能让它适应你更复杂的情况。我不认为协程的使用会影响这一点。我认为如果您将x-access-token的值赋给self.token，它现在是Token的一个实例，那么您就完成了解决方案的大部分工作。

import random

# This way doesn't work
class MyClass:
    def __init__(self):
        self.token = random.randint(1, 100)

    def change_token(self):
        self.token = random.randint(1, 100)

c = MyClass()
a = c.token
for _ in range(10):
    c.change_token()
    print(a, c.token)  # a does not change when c.token does

# This works
class Token:
    def __init__(self, n):
        self.token = n

    def __repr__(self):
        return str(self.token)

    def set_token(self, n):
        self.token = n

class MyClass2:
    def __init__(self):
        self.token = Token(random.randint(1, 100))

    def change_token(self):
        self.token.set_token(random.randint(1, 100))

print()
c = MyClass2()
a = c.token
for _ in range(10):
    c.change_token()
    print(a, c.token)  # a and c.token are the same object