[Term Entry] Python Keyword: async

content/python/concepts/keywords/terms/async/async.md

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+---
+Title: 'async'
+Description: 'Allows users to define an asynchronous function in Python.' 
+Subjects: 
+  - 'Computer Science'
+  - 'Data Science'
+Tags: 
+  - 'Async Await'
+  - 'Functions'
+  - 'Python'
+CatalogContent: 
+  - 'learn-python-3'
+  - 'paths/computer-science'
+---
+
+The **`async`** keyword defines an asynchronous function in Python. Asynchronous functions let a program handle multiple tasks concurrently without waiting for each to finish, improving efficiency and enabling non-blocking execution.
+
+## Syntax
+
+```pseudo
+import asyncio
+
+async def function_name(parameters):
+  # Function body
+  await #awaitable code
+```
+
+In the syntax:
+
+- `import asyncio`: Imports Python’s built-in library for running and managing asynchronous tasks.
+- `async`: The `async` keyword is declared before [`def`](https://www.codecademy.com/resources/docs/python/keywords/def) to define an asynchronous function (coroutine).
+- `await`: Used inside an async function to pause execution until the awaited coroutine or awaitable object completes.
+
+**Parameters:**
+
+Same as a regular function, any number of positional or keyword arguments.
+
+**Return value:**
+
+Returns a coroutine object, which must be awaited (using `await`) to get the actual result.
+
+> **Note:** If an `async` function doesn’t contain any `await` statements, it will still be valid but won’t perform any asynchronous operations.
+
+## Example 1
+
+In this example, the async function `hello()` prints the first half of 'Hello world!', waits 3 seconds, and then prints the second half:
+
+```py
+import asyncio
+
+async def hello():
+   print("Hello")
+   await asyncio.sleep(3) # Pauses for 3 seconds
+   print("world!")
+```
+
+Here is the output of this code:
+
+```shell
+Hello
+world!
+```
+
+## Example 2
+
+In this example, the `brew_tea` and `make_toast` async functions start running at the same time. `make_toast` finishes first in 3 seconds, while `brew_tea` takes 5 seconds to complete. The program waits for both tasks to finish, then prints their results together after a total of 5 seconds:
+
+```py
+import asyncio
+
+async def brew_tea():
+  print("Start brewing tea")
+  await asyncio.sleep(5) # Pauses for 5 seconds
+  return "The tea is ready!"
+
+async def make_toast():
+  print("Start making toast")
+  await asyncio.sleep(3) # Pauses for 3 seconds
+  return "The toast is ready!"
+
+async def make_breakfast():
+  batch = asyncio.gather(brew_tea(), make_toast())
+  tea_complete, toast_complete = await batch
+  print(tea_complete)
+  print(toast_complete)
+
+result = asyncio.run(make_breakfast())
+print(result)
+```
+
+The output of this code is:
+
+```shell
+Start brewing tea
+Start making toast
+The tea is ready!
+The toast is ready!
+None
+```