Why do I have to press Ctrl+D twice to close stdin?

Question

I have the following Python script that reads numbers and outputs an error if the input is not a number.

import fileinput
import sys
for line in (txt.strip()         


        

Answer 1

The first time it considers it to be input, the second time it's for keeps!

This only occurs when the input is from a tty. It is likely because of the terminal settings where characters are buffered until a newline (carriage return) is entered.