Redirecting Stdout to "Nothing" in Python

Redirecting stdout to nothing in python

Cross-platform:

import os
import sys
f = open(os.devnull, 'w')
sys.stdout = f

On Windows:

f = open('nul', 'w')
sys.stdout = f

On Linux:

f = open('/dev/null', 'w')
sys.stdout = f

Redirect stdout to a file in Python?

If you want to do the redirection within the Python script, setting sys.stdout to a file object does the trick:

# for python3
import sys
with open('file', 'w') as sys.stdout:
    print('test')

A far more common method is to use shell redirection when executing (same on Windows and Linux):

$ python3 foo.py > file

How to output a single print statement out of many and redirect the rest to null in python

Perhaps set sys.stdout to /dev/null during the timeit?

Try it online!

if __name__ == "__main__":
    from timeit import timeit
    import sys

    matrix = [[10, 20, 30, 40], [15, 15, 25, 55], [17, 19, 17, 18], [1, 8, 9, 2]]
    stdout = sys.stdout
    with open('/dev/null', 'w') as sys.stdout:
        t = timeit(lambda: method1(4, 4, matrix), number=10000)
    sys.stdout = stdout
    print(t)  # <-- 3

Temporarily Redirect stdout/stderr

To solve the issue that some function might have cached sys.stdout stream as a local variable and therefore replacing the global sys.stdout won't work inside that function, you could redirect at a file descriptor level (sys.stdout.fileno()) e.g.:

from __future__ import print_function
import os
import sys

def some_function_with_cached_sys_stdout(stdout=sys.stdout):
    print('cached stdout', file=stdout)

with stdout_redirected(to=os.devnull), merged_stderr_stdout():
    print('stdout goes to devnull')
    some_function_with_cached_sys_stdout()
    print('stderr also goes to stdout that goes to devnull', file=sys.stderr)
print('stdout is back')
some_function_with_cached_sys_stdout()
print('stderr is back', file=sys.stderr)

stdout_redirected() redirects all output for sys.stdout.fileno() to a given filename, file object, or file descriptor (os.devnull in the example).

stdout_redirected() and merged_stderr_stdout() are defined here.

Can I redirect the stdout into some sort of string buffer?

from cStringIO import StringIO # Python3 use: from io import StringIO
import sys

old_stdout = sys.stdout
sys.stdout = mystdout = StringIO()

# blah blah lots of code ...

sys.stdout = old_stdout

# examine mystdout.getvalue()

Python-Undoing stdout redirect

import os
import sys

f = open(os.devnull, 'w')
x = sys.stdout # save sys.stdout
sys.stdout = f

print("a")

sys.stdout = x # re-assign sys.stdout
print("b") # print 'b'

Send `exec()` output to another stream without redirecting stdout

If you're dead set on having a single process, then depending on how willing you are to dive into obscure C-level features of the CPython implementation, you might try looking into subinterpreters. Those are, as far as I know, the highest level of isolation CPython provides in a single process, and they allow things like separate sys.stdout objects for separate subinterpreters.

Can I redirect all output to /dev/null from within python?

import sys
old_stdout, old_stderr = sys.stdout, sys.stderr
sys.stdout = open('/dev/null', 'w')
sys.stderr = open('/dev/null', 'w')

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