from sys import stdin
from sys import stdout
upper = True
while (True):
    char = stdin.read(1)
    if (not char):
        break;
    elif (65 <= ord(char) <= 90):
        if (upper):
            upper = False
            stdout.write(char)
        else:
            stdout.write(char.lower())
    else:
        stdout.write(char)
        if (char == "." or char == "!" or char == "?"):
            upper = True

Brackets are unnecessary after while/if.

Edited by author 05.07.2019 19:38

Great program!