[Python] Import prints, even when stdout and stderr are suppressed

I have a module that I need to use. However, when it is imported, it helpfully prints out some status information.

> import problematic_module
Connected to local cache!
Detected version 1.0.0!
<several more lines of startup info>
>


I want to suppress this, so a CLI tool does not have unnecessary cruft surrounding the output. There are many questions about how to suppress console output, and a popular solution is something like this.:

import contextlib
import os
import sys

@contextlib.contextmanager
def silent_legacy_startup():
try:
old_stdout = sys.__stdout__
old_stderr = sys.__stderr__
with open(os.devnull, "w") as devnull:
with contextlib.redirect_stdout(devnull):
with contextlib.redirect_stderr(devnull):

sys.__stdout__ = devnull
sys.__stderr__ = devnull

# PLEASE BE QUIET.
yield
finally:
sys.__stdout__ = old_stdout
sys.__stderr__ = old_stderr

with silent_legacy_startup():
import problematic_module


While this makes the module import quieter, it still manages to print:

Connected to local cache!
Detected version 1.0.0!


The offending text is coming from stdout:

$ python silently_import.py 1> stdout.txt 2> stderr.txt
$ cat stdout.txt
Connected to local cache!
Detected version 1.0.0!
$ cat stderr.txt
$

Partial solution:


Since redirection silences the output, the obvious step seems to be to redirect fd 1 itself. E.g., dup2(1, 5), dup2(NULL, 1), dup2(5, 1) to restore stdout once done. Here's my attempt at that:

def noisy_code():
print("hello from print!")
sys.stdout.write("hello from stdout!\n")
sys.__stdout__.write("hello from __stdout__!\n")
with os.fdopen(1, 'w') as fd_1:
fd_1.write("hello from fdopen(1)!\n")

@contextlib.contextmanager
def silence_everything():
try:
stdout_fd = sys.stdout.fileno()
dup_stdout = os.dup(stdout_fd)
with open(os.devnull, "w") as devnull:
os.dup2(devnull.fileno(), stdout_fd)
yield
finally:
os.dup2(dup_stdout, stdout_fd)
os.close(dup_stdout)

with silence_everything():
noisy_code()


Unfortunately, this crashes, printing:

Traceback (most recent call last):
...
print("hello from print!")
OSError: [WinError 1] Incorrect function


My guess is that this style of dup2 swapping is a unix-only trick and I'm missing the windows equivalent.

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