why does python console run differently to idle

Question

Can anyone tell me why this code runs differently in python console than IDLE?

print('Do not press enter before the program says go.\n', end = '')
try:
    while True:
        input('Ready?')
        print('Starting', end = '')
        for i in range(secrets.randbits(3)):
            time.sleep(1)
            print(' .', end = '')
        now = datetime.datetime.now()
        input('\nGo!')
        print('\nReaction: {}'.format(datetime.datetime.now()-now))
except KeyboardInterrupt:
    print('Exiting.')

This is the output in IDLE which works the way I expect:

Do not press enter before the program says go.
Ready?
Starting . .
Go!

Reaction: 0:00:00.328174

But when in the console I get the same overall output but the dots do not show up one after the other, instead they all appear at once with go.Can anyone explain this strange behaviour. I am running Python 3.6.2 if that helps.

I do have a way to test if the program is running from IDLE or not which returns true if in idle and false if not in idle:

def inIDLE():
    import sys
    if 'idlelib.run' in sys.modules:
        return True
    else:
        return False

IDLE has a few quirks; the plain console is behaving correctly. If you don't want your dots to appear all at once you can tell the console to flush its output: `print(' .', end = '', flush=True)` — PM 2Ring, Sep 30 '17 at 06:21
Ahh, now that is the solution that I was looking for. I had no idea how to use flush but now I do. Thanks for the help @PM2Ring — Lasagnenator, Sep 30 '17 at 10:50

score 1 · Accepted Answer · answered Sep 30 '17 at 06:43

Because it's a GUI program (running on Tkinter) IDLE has a few quirks; the plain console is actually behaving correctly, since output to stdout is normally line-buffered.

If you don't want your dots to appear all at once you can tell the console to flush its output:

print(' .', end = '', flush=True)

Alternatively, you can print to stderr which is normally not buffered:

import sys
#...
print(' .', end = '', file=sys.stderr)

In the console, you can select unbuffered stdout by passing the -u option to the interpreter, see python3 -h for details.

why does python console run differently to idle

1 Answers1