如何在python 2和3中都覆盖？

Question

I'm trying to write a simple program that will display a rotating loading icon in the terminal that is compatible with both python 2.7 and 3.3. I would have though the from __future__ import print_function statement would work but all I get in python 2 is a blank line. I then tried sys.stdout.write but that also comes up blank.

Here is my reduced code:

from __future__ import print_function
import time
import sys
import itertools

def load_icon(pause=0.5, timeout=None):
    tic = time.time()
    try:
        while (not timeout) or timeout < time.time() - tic:
            for symbol in itertools.cycle('\|/-'):
                ##print('\r{} '.format(symbol), end='') # Old version
                sys.stdout.write('\r{} '.format(symbol)) # New
                # Neither of the above work in py 2.7 yet do in py 3.3
                time.sleep(pause)
    except KeyboardInterrupt:
        pass
    finally:
        sys.stdout.write('\r    \n')

if __name__ == '__main__':
    load_icon(*[float(arg) for arg in sys.argv[1:]])

and this is the result:

$ python3 load_icon.py
/
$ # a rotating line
$ python2 load_icon.py

$ # nothing shown

Is there a way to solve this without creating two seperate files for each version? I am running this on linux centOS6 with python 2.7.8 and 3.3.1. Thanks in advance.

Answer 1

Explicitly flush ing sys.stdout seems to fix it in Python 2:

            sys.stdout.write('\r{} '.format(symbol))
            sys.stdout.flush()

The print function also has a flush parameter:

            print('\r{} '.format(symbol), end='', flush=True)

However, this seems to work only in Python 3. The version of print imported with from __future__ import print_function seems to be missing this parameter.