Question

I’ve been trying to print out the progress of a for loop in python2.7 using the following code:

for i in range(100):
    if float(i) % 10.0 == 0:
        print i, "\r",

The behaviour I’m after is the refreshing of the same line on std out rather than writing to a new line every time.

EDIT 1:

Testing in my console (Xfce Terminal 0.4.8), I actually don’t get any output regardless of whether I include the if statement or not.

Why is there no output?

I originally said the behaviour of the stdout changed depending on the if statement being there or not because I simplified the code that produced the problem to its most simple form (only to produce the above mentioned effect). My apologies.

EDIT 2:

Thanks to senderle, this is solved. If you miss out the sleep() command, the prints and carriage return happen so quickly you can’t see them.

EDIT 3:

One last thing. If you don’t catch for the final number in range(100), i.e. 99, the number is cleared off the screen.

EDIT 4:

Note the comma after print i in senderle‘s answer.

Answer 1

I have found that using sys.stdout is a more system-independent way of doing this, for varions reasons having to do with the way print works. But you have to flush the buffer explicitly, so I put it in a function.

def carriage_return():
    sys.stdout.write('\r')
    sys.stdout.flush()

This is kind of a WAG. Let me know if it helps.

I tried this and it works for me. The time.sleep is just for dramatization.

import sys, time

def carriage_return():
    sys.stdout.write('\r')
    sys.stdout.flush()

for i in range(100):
    if i % 10 == 0:
        print i,
        carriage_return()
        time.sleep(1)

Finally, I have seen people do this as well. Using terminal control codes like this seems right in some ways, but it also seems more brittle to me. This works for me with the above code as well (on OS X).

def carriage_return():
    if sys.platform.lower().startswith('win'):
        print '\r'
    else:
        print chr(27) + '[A'