Python3 sleep() problem

Question

I was writing a simple program on Python 3.1 and I stumbled upon this:

If I run this on the IDLE it works as intended - prints "Initializing." and then adds two dots, one after each second, and waits for input.

from time import sleep

def initialize():
    print('Initializing.', end='')
    sleep(1)
    print(" .", end='')
    sleep(1)
    print(" .", end='')
    input()

initialize()

The problem is that when I double-click the .py to execute the file, it runs on python.exe instead of pythonw.exe, and strange things happen: it joins all the sleep() times i.e. makes me wait for 2 seconds, and then prints the whole string Initializing. . . at once. Why does this happen? Is there a way to avoid that happening in the terminal? It works fine if I use the IDLE in both windows and linux.

I imagine the reason it's buffering is because you haven't given it a \n yet. In general the use of end will indicate you're going on and writing something immediately. — Chris Morgan
– Chris Morgan, Commented Dec 16, 2010 at 3:25

John La Rooy · Accepted Answer · 2010-12-16 01:17:45Z

24

This is because the output is being buffered.

You should add a sys.stdout.flush() after each write

answered Dec 16, 2010 at 1:17

John La Rooy

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2 Comments

roddds Over a year ago

And, after 4 years, I just noticed I never actually set this as an accepted answer.

tobias_k Over a year ago

Using Python 3's print function, you can also use the flush parameter, e.g. print(" .", end='', flush=True)

Community · Accepted Answer · 2017-05-23 12:00:34Z

5

It sounds like the difference is that stdout is automatically being flushed in IDLE. For efficiency, programming languages often save up a bunch of print calls before writing to the screen, which is a slow process.

Here's another question that has the answer you need: How to flush output of Python print?

edited May 23, 2017 at 12:00

CommunityBot

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answered Dec 16, 2010 at 1:16

leoger

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