In Python, why won't something print without a newline?

Question

import time
import sys
sys.stdout.write("1")
time.sleep(5)
print("2")

will print "12" after 5 seconds

import time
import sys
sys.stdout.write("1\n")
time.sleep(5)
print("2")

will print "1\n" right away, then "2" after 5 seconds

Why is this?

Answer 1

If you add "\n" then stream is flushed automaticaly, and it is not without new line at the end. You can flush output with:

sys.stdout.flush()

Answer 2

Because stdout is buffered. You may be able to force the output sooner with a sys.stdout.flush() call.