how to capture stdout & stderr

capture.py

from __future__ import print_function

import contextlib
import sys
from cStringIO import StringIO


def print_error(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)


@contextlib.contextmanager
def capture():
    out_ = sys.stdout
    err_ = sys.stderr
    try:
        out = [StringIO(), StringIO()]
        sys.stdout, sys.stderr = out
        yield out
    finally:
        sys.stdout = out_
        sys.stderr = err_
        out[0] = out[0].getvalue()
        out[1] = out[1].getvalue()


if __name__ == "__main__":
    with capture() as out_err:
        print('hello out')
        print_error('hello err')
    print(out_err)  # ['hello out\n', 'hello err\n']