Why does input() read characters typed during time.sleep() in a terminal program?

Question:
I’m writing a simple terminal-based program in Python and noticed unexpected behavior when combining time.sleep() and input().

Here is a minimal example:

import time print("Starting") time.sleep(3) input()

If I type characters while the program is in the time.sleep(3) call, those characters are immediately read by input() once the sleep finishes. I expected input() to only accept input typed after it is called.

Why does this happen? Is the input being handled by Python, or is it buffered by the terminal or operating system? What is the correct way to prevent previously typed input from being consumed by input() in terminal-based programs?

I’m especially interested in understanding the underlying reason for this behavior, not just a workaround.

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