await in python

await keyword is used to pause the execution of a task until the result of another task or operation is ready. It's a key part of Python's asynchronous programming, allowing for non-blocking, concurrent execution of I/O-bound tasks.

import asyncio

async def fun():
    print("Hello")
    await asyncio.sleep(1) 
    print("World")

asyncio.run(fun())

Hello
World

Explanation:

• await asyncio.sleep(1) pauses the execution for 1 second without blocking other tasks, allowing the event loop to run other asynchronous operations.
• After the pause, print("World") executes, demonstrating the non-blocking behavior enabled by await.

Syntax

await <expression>

• Parameters: expression - An awaitable object, such as a coroutine, an asynchronous function, or any object that supports asynchronous operations (e.g., asyncio.sleep(), a Future object).
• Returns: It returns the result of the awaited task or coroutine once it has finished executing.

Examples

Example 1: This example demonstrates how to run two tasks concurrently using Python's asyncio library.

import asyncio

async def task_1():
    print("Task 1 started")
    await asyncio.sleep(2)  
    print("Task 1 completed")

async def task_2():
    print("Task 2 started")
    await asyncio.sleep(1) 
    print("Task 2 completed")

async def main():
    await asyncio.gather(task_1(), task_2()) 

asyncio.run(main())

Task 1 started
Task 2 started
Task 2 completed
Task 1 completed

Explanation:

• asyncio.gather() starts both coroutines concurrently.
• Since task_2() waits for 1 second and task_1() waits for 2 seconds, task_2() completes first, followed by task_1().
• This demonstrates how await allows multiple asynchronous tasks to make progress without blocking each other.

Example 2: This example shows how await can be used to execute asynchronous tasks one after another. The second task starts only after the first task finishes.

import asyncio

async def custom_async_task(task_num):
    print(f"Task {task_num} started")
    await asyncio.sleep(3)
    print(f"Task {task_num} completed")

async def main():
    await custom_async_task(1)
    await custom_async_task(2)

asyncio.run(main())

Output

Task 1 started
Task 1 completed
Task 2 started
Task 2 completed

Explanation:

• await custom_async_task(1) pauses main() until Task 1 completes.
• Only then does await custom_async_task(2) start Task 2.
• Although the tasks are asynchronous, they execute sequentially because each task is awaited before the next one begins.