In what cases is multithreading used in programming?

Multithreading is used when it is necessary to perform multiple tasks simultaneously to improve the performance or responsiveness of a program. In Python, this is useful for:

• Performing input/output operations (such as network requests, file handling), where threads can wait for operations to complete without blocking the entire program.
• Parallel processing of tasks that do not require intensive computation (due to GIL in CPython).
• Improving the responsiveness of user interfaces so that heavy operations do not block the main thread.

An example of using multithreading for parallel downloading of multiple files:

import threading
import requests

def download(url):
    resp = requests.get(url)
    print(f"Downloaded {len(resp.content)} bytes from {url}")

urls = ["https://example.com/file1", "https://example.com/file2"]
threads = []
for url in urls:
    t = threading.Thread(target=download, args=(url,))
    t.start()
    threads.append(t)

for t in threads:
    t.join()