[Tut] Python Async Function - Printable Version

[Tut] Python Async Function - Printable Version

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[Tut] Python Async Function - xSicKxBot - 05-08-2023

Python Async Function

5/5 – (1 vote)

As a Python developer, you might have encountered the terms

Code:
async

and

Code:
await

, wondering what they are and how to use them in your projects.

Async functions enable you to write concurrent code using the

Code:
async

Code:
await

syntax. This powerful duo allows you to perform multiple tasks simultaneously without blocking the execution of your code.

Think of it as having multiple browser tabs open; while one page loads, you can continue browsing other tabs. This capability means your Python applications can become faster, more efficient, and capable of handling many I/O operations.

To get started with

Code:
async

functions, you’ll need to get acquainted with Python’s

Code:
asyncio

library, which serves as a foundation for numerous asynchronous frameworks such as high-performance network and web servers, database connection libraries, and distributed task queues.

Mastering async functions can truly elevate your Python programming skills and help you build powerful and responsive applications.

Python Async Function Basics

[Image: image-80.png]

First, you’ll learn the basics of Python

Code:
async

functions, which can help improve the performance of your asynchronous programming.

We’ll cover

async functions without
Code:
await
,
an async function example, async function return, and
async function call.

Async Function Without Await

You might wonder if it’s possible to create an async function without using the

Code:
await

keyword. Well, it is!

However, without

Code:
await

, the async function becomes somewhat less useful, since you won’t be able to pause its execution and yield control back to the event loop.

This means your async code will not be able to achieve cooperative concurrency, and other coroutines might be stuck waiting for their turn to execute. It’s generally a good idea to use

Code:
await

when working with async functions for more efficient asynchronous programming.

Async Function Example

Let’s dive into a simple example of using an async function in Python with

Code:
asyncio

Code:
import asyncio async def greet(name: str): print(f"Hello, {name}!") await asyncio.sleep(1) print(f"Nice to meet you, {name}!") async def main(): task1 = asyncio.create_task(greet("Alice")) task2 = asyncio.create_task(greet("Bob")) await task1 await task2 asyncio.run(main())

In this example, an async function

Code:
greet

is declared, which prints a greeting message, waits for 1 second using

Code:
asyncio.sleep

, and then prints another message.

The

Code:
main

asynchronous function creates two tasks to call

Code:
greet

with different names, running them concurrently.

Async Function Return

When you want to return a value from an async function, just use the

Code:
return

statement as you would in regular functions. However, keep in mind that the returned value will be wrapped in an

Code:
asyncio.Future

object, not the actual value.

You’ll need to use

Code:
await

to get the value when calling this async function.

For example:

Code:
async def calculate_result(): await asyncio.sleep(1) return "Result!" async def main(): result = await calculate_result() print(result) asyncio.run(main())

Here,

Code:
calculate_result

is an async function that returns a value after asynchronously waiting for 1 second. In the

Code:
main()

function, you can use

Code:
await

to get the actual value and print it.

Async Function Call

To call an async function, you can’t simply use the normal function call syntax, because doing so would just return a coroutine object, not the actual result of the function. Instead, you have to use the

Code:
await

keyword to call the async function, or use

Code:
asyncio.create_task

or similar functions to run it concurrently:

Code:
# Using `await` to call async function
result = await async_function() # Using `asyncio.create_task` to run concurrently
task = asyncio.create_task(async_function())

Remember to always use the appropriate method to call your async functions in order to achieve efficient asynchronous programming with Python’s powerful

Code:
async/await

syntax.

Advanced Async Function Concepts

[Image: image-81.png]

Next, you’ll explore advanced async function concepts to give you a better understanding of how they work in Python.

Ready? Let’s dive in!

Async Function Decorator

To create an async function, you’ll use the

Code:
async def

syntax. This means you don’t have to use a decorator, but you can still decorate asynchronous functions with the

Code:
@some_decorator

syntax for better modularity in your programs.

For instance, consider using

Code:
@asyncio.coroutine

with a

Code:
yield from

syntax if you’re working with Python 3.4 or earlier. Or simply upgrade to newer versions!

Async Function Type Hint

Type hints help improve the readability of your async code. Specify the input and output types of your async function using the

Code:
typing

module’s Coroutine and

Code:
asyncio

‘s Future objects.

Here’s an example:

Code:
from typing import Coroutine
import asyncio async def some_async_function() -> Coroutine[str]: await asyncio.sleep(1) return "done"

Async Function Returns Coroutine

An async function, also known as a coroutine, returns a coroutine object when called. You can use it as a direct call or pass it to an event loop to run the async function using

Code:
asyncio.run()

Code:
loop.run_until_complete()

.

Keep in mind coroutine objects aren’t executed until you explicitly use an event loop or an

Code:
await

expression.

Async Function Await

When writing async functions, the

Code:
await

keyword is crucial. It allows you to pause the execution of a coroutine and wait for a result without blocking other coroutines.

You’ll often use

Code:
await

with I/O-bound operations, like reading from files, interacting with network services, or retrieving resources, which can take a significant amount of time.

Recommended: Python

Code:
__await()__

Magic Method

Async Function Type

An async function’s type is

Code:
coroutine

. So when defining your async function, you’re essentially creating a non-blocking function that allows other functions to run while it waits for results.

To check if an object in Python is a coroutine, you can use

Code:
inspect.iscoroutine(obj)

Code:
inspect.iscoroutinefunction(obj)

.

Async Function Return Type

Async functions return a

Code:
coroutine

object, but you can also specify the type of the eventual returned value. For instance, if your async function performs some networking tasks and returns JSON data, you can specify the return type as

Code:
Dict[str, Any]

.

Here’s how you do that:

Code:
from typing import Dict, Any, Coroutine
import asyncio async def fetch_json_data() -> Coroutine[Dict[str, Any]]: # some networking tasks here await asyncio.sleep(2) return {"key": "value"}

Async Function in Different Contexts

[Image: image-82.png]

In this section, we will explore using async functions in different circumstances, such as within classes, threads, and converting async functions to sync. We will also discuss the concepts of async function sleep and handling functions that were never awaited.

Async Function in Class

When working with classes in Python, you might want to include asynchronous methods. To achieve this, just define your class method with

Code:
async def

. Remember to

Code:
await

your async methods when calling them to ensure proper execution.

Here’s an example:

Code:
class MyClass: async def my_async_method(self): await asyncio.sleep(1) async def main(): my_obj = MyClass() await my_obj.my_async_method()

Async Function in Thread

Running async functions in a thread can be tricky due to event loop requirements. Use

Code:
asyncio.to_thread()

for running async functions in threads. This will ensure your async function is executed within the correct thread’s event loop.

For example:

Code:
async def my_async_function(): await asyncio.sleep(1) print("Hello from async function!") async def main(): result = await asyncio.to_thread(my_async_function)

Async Function to Sync

If you need to call an async function from synchronous code, you can use

Code:
asyncio.run()

or create an event loop that runs a given coroutine.

Here’s an example of how to run an async function from sync code:

Code:
def sync_function(): asyncio.run(my_async_function())

Async Function Sleep

Sometimes, you might want to introduce a delay in your coroutine using

Code:
asyncio.sleep

. This allows other coroutines to run while waiting for IO operations or other events.

Example:

Code:
async def delayed_hello(): await asyncio.sleep(1) print("Hello after 1 second!")

Recommended: Time Delay in Python

Async Function Was Never Awaited

In some cases, you may forget to

Code:
await

an async function, which leads to warnings such as

Code:
"coroutine 'my_async_function' was never awaited."

To prevent these issues, always ensure you’re using

Code:
await

when calling async functions:

Code:
async def my_async_function(): await asyncio.sleep(1) async def main(): # Missing 'await' would lead to a warning await my_async_function()

If you got something out of this article, I’m sure you’ll learn something of this one:

Recommended: Python Async With Statement — Simplifying Asynchronous Code

I promise it has more beautiful pics.