Suppress stdout / stderr print from Python functions

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As of python 3.5 we can do this with minimal work using built-ins in contextlib, namely redirect_stdout and redirect_stderr. We only need to combine these two built-in context managers in a custom context manager of ours, which can be easily done using the nice pattern in Martijn’s answer here. Redirecting both outputs to os.devnull should be safe and portable enough.

from contextlib import contextmanager,redirect_stderr,redirect_stdout
from os import devnull

@contextmanager
def suppress_stdout_stderr():
    """A context manager that redirects stdout and stderr to devnull"""
    with open(devnull, 'w') as fnull:
        with redirect_stderr(fnull) as err, redirect_stdout(fnull) as out:
            yield (err, out)

Note that suppressing stderr will still give you full tracebacks when something breaks, which is a good thing:

import sys

def rogue_function():
    print('spam to stdout')
    print('important warning', file=sys.stderr)
    1 + 'a'
    return 42

with suppress_stdout_stderr():
    rogue_function()

When run the above only prints

Traceback (most recent call last):
  File "tmp.py", line 20, in <module>
    rogue_function()
  File "foo.py", line 16, in rogue_function
    1 + 'a'
TypeError: unsupported operand type(s) for +: 'int' and 'str'

to the terminal. Unhandled exceptions should never go unnoticed.

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