Consider the following program:

import time

from tqdm import tqdm

with tqdm(range(5)) as bar:
    for i in bar:
        bar.write(str(i))
        time.sleep(1)

On Python 2.7, it does exactly what you’d expect.

On Python 3 (at least 3.5 and 3.6), the bar is not drawn until it’s closed.

If you move the bar.write() behind the time.sleep(1), it works on Python 3 too.

Some kind of race condition?