How to Temporarily Redirect stdout/stderr in Python Methods Without Affecting Local Stream Copies?

Temporarily Redirect stdout/stderr in a Method: Imperfect Current Solutions

The issue with existing solutions for temporarily redirecting stdout/stderr in Python lies in their inability to redirect; instead, they replace streams entirely. This becomes problematic when methods possess local copies of streams (e.g., passed as parameters), rendering the redirection ineffective.

Solution via Contextmanager

An alternative approach involves utilizing a contextmanager to encapsulate the redirection logic. This approach ensures that the redirection is only active within the context, without affecting local stream copies:

<code class="python">import os
import sys

class RedirectStdStreams(object):
    def __init__(self, stdout=None, stderr=None):
        self._stdout = stdout or sys.stdout
        self._stderr = stderr or sys.stderr

    def __enter__(self):
        self.old_stdout, self.old_stderr = sys.stdout, sys.stderr
        self.old_stdout.flush(); self.old_stderr.flush()
        sys.stdout, sys.stderr = self._stdout, self._stderr

    def __exit__(self, exc_type, exc_value, traceback):
        self._stdout.flush(); self._stderr.flush()
        sys.stdout = self.old_stdout
        sys.stderr = self.old_stderr

if __name__ == '__main__':

    devnull = open(os.devnull, 'w')
    print('Fubar')

    with RedirectStdStreams(stdout=devnull, stderr=devnull):
        print("You'll never see me")

    print("I'm back!")</code>

In this example, the RedirectStdStreams class is designed to redirect both stdout and stderr to a specified destination (e.g., /dev/null) within a defined context. This approach effectively redirects streams without interrupting local stream copies.

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