Redirecting stdout to "nothing" in python

I have a large project consisting of sufficiently large number of modules, each printing something to the standard output. Now as the project has grown in size, there are large no. of print statements printing a lot on the std out which has made the program considerably slower.

So, I now want to decide at runtime whether or not to print anything to the stdout. I cannot make changes in the modules as there are plenty of them. (I know I can redirect the stdout to a file but even this is considerably slow.)

So my question is how do I redirect the stdout to nothing ie how do I make the print statement do nothing?

# I want to do something like this.
sys.stdout = None         # this obviously will give an error as Nonetype object does not have any write method.

Currently the only idea I have is to make a class which has a write method (which does nothing) and redirect the stdout to an instance of this class.

class DontPrint(object):
    def write(*args): pass

dp = DontPrint()
sys.stdout = dp

Is there an inbuilt mechanism in python for this? Or is there something better than this?

Solution 1:

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

Solution 2:

A nice way to do this is to create a small context processor that you wrap your prints in. You then just use is in a with-statement to silence all output.

Python 2:

import os
import sys
from contextlib import contextmanager

@contextmanager
def silence_stdout():
    old_target = sys.stdout
    try:
        with open(os.devnull, "w") as new_target:
            sys.stdout = new_target
            yield new_target
    finally:
        sys.stdout = old_target

with silence_stdout():
    print("will not print")

print("this will print")

Python 3.4+:

Python 3.4 has a context processor like this built-in, so you can simply use contextlib like this:

import contextlib

with contextlib.redirect_stdout(None):
    print("will not print")

print("this will print")

If the code you want to surpress writes directly to sys.stdout using None as redirect target won't work. Instead you can use:

import contextlib
import sys
import os

with contextlib.redirect_stdout(open(os.devnull, 'w')):
    sys.stdout.write("will not print")

sys.stdout.write("this will print")

If your code writes to stderr instead of stdout, you can use contextlib.redirect_stderr instead of redirect_stdout.

Running this code only prints the second line of output, not the first:

$ python test.py
this will print

This works cross-platform (Windows + Linux + Mac OSX), and is cleaner than the ones other answers imho.

Solution 3:

If you're in python 3.4 or higher, there's a simple and safe solution using the standard library:

import contextlib

with contextlib.redirect_stdout(None):
  print("This won't print!")