changing stdout and stderr

[Skaperen]

inside a module i want to change where stdout and stderr go to. i had several ideas but nothing worked. i can't find anything about how to do this in the manual. the latest i tried was to change file descriptors 1 and 2 but that only left me with the file i opened being empty.

[bowlofred]

Which stdout/stderr? Changing them by assigning to sys.stdout/sys.stderr should work the same in a module as it does in the main program.

redirect.py

import sys

def redirect(outname, errname):
    sys.stdout = open(outname, "w")
    sys.stderr = open(errname, "w")
    return

Main program that calls the module:

import redirect

print("hello")        # goes to stdout
redirect.redirect("/tmp/redirected.out", "/tmp/redirected.err")
print("hello, there") # should go to redirected stdout
5/0                   # error should go to redirected stderr

Output:
$ python3 test.py
hello
$ cat /tmp/redirected.out
hello, there
$ cat /tmp/redirected.err
Traceback (most recent call last):
  File "test.py", line 6, in <module>
    5/0                   # error should go to redirected stderr
ZeroDivisionError: division by zero

[Skaperen]

Which stdout/stderr?

both!

i tried something like your redirect.py, replacing them with the opened file reference but nothing was output. i concluded they were cached somewhere. i even tried closing them in advance.

[bowlofred]

By which, I was trying to make sure you were talking about the stdout/stderr of the python process and not of some calling shell or called subprocess.

Is the console still getting the data? If not, then the redirection has worked. Need to figure out why it's not being written. Have you tried with unbuffered output (like running with -u or putting a flush into the print() function?)

[Skaperen]

i redirected to a file and did output. i got nothing on the console and an empty file. i concluded that it did something but not the right thing. i should have gotten the output in the file.