Suggestion: Add more examples for “Type Hinting Asynchronous Objects” section in chapter 21

[kamalfarahani]

Dear Ramalho,

I hope you are well. I'm writing to suggest an improvement for the “Type Hinting Asynchronous Objects” section in Chapter 21 for the next edition.

Enhancing Clarity with Examples

I believe that including additional examples in this section would significantly enhance understanding of how to properly use type hints for asynchronous objects. Here are some specific suggestions:

• Coroutines Example: A beneficial addition would be an example demonstrating type hints for coroutines. The following code showcases how to achieve this:

import asyncio
import socket

from collections.abc import AsyncGenerator, Generator, Coroutine, Callable


def get_ipv4_by_hostname(hostname: str) -> list[str]:
 return list(
 i[4][0]
 for i in 
 socket.getaddrinfo(hostname, 0)
 if i[0] is socket.AddressFamily.AF_INET
 and i[1] is socket.SocketKind.SOCK_RAW 
 )


async def get_ipv4_by_hostname_async(hostname: str) -> list[str]:
 return await asyncio.to_thread(get_ipv4_by_hostname, hostname)


async def print_domanin_ip(
 domain: str,
 get_ip: Callable[[str], Coroutine[None, None, list[str]]]) -> None:
 ips = await get_ip(domain)
 if ips:
 for ip in ips:
 print(f'{domain}: {ip}')
 else:
 print(f'{domain}: No IP found')
 print('_' * 20)


async def main() -> None:
 await print_domanin_ip('docker.com', get_ipv4_by_hostname_async)

• AsyncGenerators Example: The official typing documentation provides an excellent and clear example for AsyncGenerators. Including a similar example in the book would be valuable:

async def echo_round() -> AsyncGenerator[int, float]:
 sent = yield 0
 while sent >= 0.0:
 rounded = await round(sent)
 sent = yield rounded

I also guess that there might be a typo on the page 825, the image is provided below:

I think “to last” phrase should be removed because Coroutine is actually covariant on the third parameter.