Event Loop

Introduction

The event loop is the core of asyncio - it runs async tasks, handles I/O, and schedules callbacks. Understanding event loop is essential for async programming.

Running the Event Loop

import asyncio

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

# Python 3.7+
asyncio.run(my_task())

# Older method
loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(my_task())
finally:
    loop.close()

get_event_loop

import asyncio

def main():
    loop = asyncio.get_event_loop()
    loop.run_until_complete(asyncio.sleep(1))

# In async context
async def async_main():
    loop = asyncio.get_running_loop()
    task = loop.create_task(asyncio.sleep(1))
    await task

create_task

import asyncio

async def task1():
    await asyncio.sleep(1)
    return "Task 1 done"

async def task2():
    await asyncio.sleep(0.5)
    return "Task 2 done"

async def main():
    loop = asyncio.get_running_loop()
    
    t1 = loop.create_task(task1())
    t2 = loop.create_task(task2())
    
    results = await asyncio.gather(t1, t2)
    print(results)

asyncio.run(main())

Scheduling Callbacks

import asyncio

def callback(name):
    print(f"Callback {name} called")

async def main():
    loop = asyncio.get_running_loop()
    
    loop.call_soon(callback, "A")
    loop.call_later(1.0, callback, "B")
    
    await asyncio.sleep(2)

Custom Event Loop

import asyncio

class CustomEventLoop(asyncio.AbstractEventLoop):
    def run_until_complete(self, future):
        # Custom implementation
        pass

# Create custom loop
loop = CustomEventLoop()
loop.run_until_complete(some_async_function())

Practice Problems

1. Run multiple async tasks concurrently
2. Use create_task with gathering
3. Schedule callbacks at different times
4. Handle event loop in different contexts
5. Create loop for specific platform