Suppress stdout / stderr print from Python functions

This approach (found through the related sidebar) might work. It reassigns the file descriptors rather than just the wrappers to them in sys.stdout, etc.

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.

python 3.6 working version, tested with million suppressions without any errors

import os
import sys

class suppress_stdout_stderr(object):
    def __enter__(self):
        self.outnull_file = open(os.devnull, 'w')
        self.errnull_file = open(os.devnull, 'w')

        self.old_stdout_fileno_undup    = sys.stdout.fileno()
        self.old_stderr_fileno_undup    = sys.stderr.fileno()

        self.old_stdout_fileno = os.dup ( sys.stdout.fileno() )
        self.old_stderr_fileno = os.dup ( sys.stderr.fileno() )

        self.old_stdout = sys.stdout
        self.old_stderr = sys.stderr

        os.dup2 ( self.outnull_file.fileno(), self.old_stdout_fileno_undup )
        os.dup2 ( self.errnull_file.fileno(), self.old_stderr_fileno_undup )

        sys.stdout = self.outnull_file        
        sys.stderr = self.errnull_file
        return self

    def __exit__(self, *_):        
        sys.stdout = self.old_stdout
        sys.stderr = self.old_stderr

        os.dup2 ( self.old_stdout_fileno, self.old_stdout_fileno_undup )
        os.dup2 ( self.old_stderr_fileno, self.old_stderr_fileno_undup )

        os.close ( self.old_stdout_fileno )
        os.close ( self.old_stderr_fileno )

        self.outnull_file.close()
        self.errnull_file.close()