Example of code for Python using asyncio to handle asynchronous programming

In Python, asynchronous programming can be usedasyncioLibrary, This library provides some tools and functions to write asynchronous code. Here are several key concepts and examples for dealing with asynchronous programming.

Key concepts

1. Asynchronous function (coroutine):useasync defDefined function.
2. Wait (await): Used inside an asynchronous functionawaitThe keyword waits for an asynchronous operation to complete.
3. Event loop: A scheduler for asynchronous operation, managing all asynchronous tasks and callbacks.
4. Task: Coroutines executed by event loop schedule.

Basic examples

Here is a simple asynchronous function example:

import asyncio

async def say_hello():
    print("Hello")
    await (1)
    print("World")

# Get the event loop and run the asynchronous function(say_hello())

In this example,say_hellois an asynchronous function that waits for a second after printing "Hello" and then prints "World".

Concurrently execute multiple asynchronous functions

Can be usedConcurrently execute multiple asynchronous functions:

import asyncio

async def say_after(delay, message):
    await (delay)
    print(message)

async def main():
    task1 = asyncio.create_task(say_after(1, "Hello"))
    task2 = asyncio.create_task(say_after(2, "World"))

    await task1
    await task2

(main())

In this example,mainThe function creates two taskstask1andtask2, and execute them concurrently.say_afterThe function prints the message after waiting for the specified time.

Asynchronous I/O operation

Asynchronous programming is especially suitable for I/O-intensive tasks such as network requests. The following is a useaiohttpExample of library performing asynchronous HTTP requests:

import aiohttp
import asyncio

async def fetch(url):
    async with () as session:
        async with (url) as response:
            return await ()

async def main():
    url = ''
    html = await fetch(url)
    print(html)

(main())

In this example,fetchFunction useaiohttpThe library performs asynchronous HTTP requests,mainFunction CallfetchAnd print the response content.

Timeout processing

Can be usedasyncio.wait_forSet timeout:

import asyncio

async def say_hello():
    await (2)
    return "Hello, World!"

async def main():
    try:
        result = await asyncio.wait_for(say_hello(), timeout=1)
        print(result)
    except :
        print("The coroutine took too long to complete")

(main())

In this example, ifsay_helloThe function does not complete within 1 second, and will be triggered。

Asynchronous context managers and iterators

Can be usedasync withandasync forHandle asynchronous context managers and iterators:

import aiohttp
import asyncio

class AsyncContextManager:
    async def __aenter__(self):
        print("Entering context")
        return self

    async def __aexit__(self, exc_type, exc, tb):
        print("Exiting context")

    async def do_something(self):
        await (1)
        print("Doing something")

async def main():
    async with AsyncContextManager() as manager:
        await manager.do_something()

(main())

In this example,AsyncContextManagerThe class implements an asynchronous context management protocol.mainFunction useasync withEnter and exit the context and call the asynchronous methoddo_something。

summary

By usingasyncioLibrary, Python provides a powerful and flexible way to handle asynchronous programming. Asynchronous programming can significantly improve the performance of I/O-intensive tasks, making code more efficient when handling multiple tasks. Mastering the basic concepts and tools of asynchronous programming will help you write high-performance asynchronous applications.

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