async/await
- Python course
- Advanced
- Lesson 25/83
- 5 min
Learn the async and await keywords.
async/await
async/await is syntax that makes concurrent code readable. You define a function with async def; inside, you wait for another concurrent operation with await.
async def greet(name):
return "Hello, " + nameCalling an async def function does not run it immediately; it returns a coroutine object. Running it needs an event loop, which we'll cover in the next lesson.
You mark waiting points with await; while waiting, the event loop can run other work.
Waiting with await
You wait for a coroutine or awaiting operation with await. It tells the event loop "I can wait here, do other work".
await is valid only inside async def; using it outside raises an error. The expression next to await must be an awaitable: a coroutine, task or future.
async def fetch():
await asyncio.sleep(1)
return "ok"Here await lets the event loop run other work while asyncio.sleep is pending.
Practice Write greet with async def
The function async def greet(name) returns "Hello, " + name. Then call print(asyncio.run(greet("Ayşe"))). Start with import asyncio.
Starter code
# import the asyncio module
# declare a coroutine named greet; return a greeting string with the name
# print the result of greet("Ayşe") via asyncio.runSample solution
import asyncio
async def greet(name):
return "Hello, " + name
print(asyncio.run(greet("Ayşe")))Expected output
Hello, Ayşe
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does an async def function return when called directly?
- It raises an error
- The function result
- None
- A coroutine object Correct answer
Explanation: Calling async def does not run it; it returns a coroutine object.
2 Complete async def
____ def greet(name):
return "Merhaba, " + nameasync def greet(name):
return "Merhaba, " + nameExplanation: async def declares a coroutine function.
3 Match the async/await concepts
| Term | Meaning |
|---|---|
async def |
Coroutine definition |
await |
Waiting point |
coroutine |
Runnable object |
event loop |
Running mechanism |