Asyncio Event Loop and Coroutines
To understand how Python's asyncio library enables asynchronous programming, you need to learn about the event loop and coroutines. The event loop is the core of asyncio. It is a loop that runs in the background, constantly looking for tasks that are ready to run, and managing when each task gets a chance to execute. Instead of running all tasks at once, the event loop schedules and switches between them, allowing your program to handle many operations seemingly at the same time—without blocking on slow operations like network requests or timers.
A coroutine is a special kind of function that can pause in the middle of its execution and give control back to the event loop. When a coroutine reaches an await statement, it tells the event loop, "Pause me here, and let something else run until I'm ready to continue." This allows your program to stay responsive and efficient, even when waiting for slow operations.
You define a coroutine using the async def syntax. To actually run a coroutine, you need to schedule it on the event loop. In modern Python, the easiest way to do this is with asyncio.run, which starts the event loop, runs your coroutine, and then closes the loop when done.
12345678import asyncio async def greet(): print("Hello...") await asyncio.sleep(1) print("...Asyncio World!") asyncio.run(greet())
In this example, the greet function is a coroutine. When you call asyncio.run(greet()), Python creates an event loop, schedules the coroutine, and runs it. The await asyncio.sleep(1) line tells the event loop to pause this task for one second, during which time the event loop could run other tasks if they existed. After the pause, the coroutine resumes and prints the second line.
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To understand how Python's asyncio library enables asynchronous programming, you need to learn about the event loop and coroutines. The event loop is the core of asyncio. It is a loop that runs in the background, constantly looking for tasks that are ready to run, and managing when each task gets a chance to execute. Instead of running all tasks at once, the event loop schedules and switches between them, allowing your program to handle many operations seemingly at the same time—without blocking on slow operations like network requests or timers.
A coroutine is a special kind of function that can pause in the middle of its execution and give control back to the event loop. When a coroutine reaches an await statement, it tells the event loop, "Pause me here, and let something else run until I'm ready to continue." This allows your program to stay responsive and efficient, even when waiting for slow operations.
You define a coroutine using the async def syntax. To actually run a coroutine, you need to schedule it on the event loop. In modern Python, the easiest way to do this is with asyncio.run, which starts the event loop, runs your coroutine, and then closes the loop when done.
12345678import asyncio async def greet(): print("Hello...") await asyncio.sleep(1) print("...Asyncio World!") asyncio.run(greet())
In this example, the greet function is a coroutine. When you call asyncio.run(greet()), Python creates an event loop, schedules the coroutine, and runs it. The await asyncio.sleep(1) line tells the event loop to pause this task for one second, during which time the event loop could run other tasks if they existed. After the pause, the coroutine resumes and prints the second line.
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