Where is the _ environment variable documented?

[yurivict]

When I run this script:

import os

for k,v in os.environ.items():
    print(f'key={k} val={v}')

it prints the environjment with an altered _ value.

The new _ value is:

key=_ val=/usr/local/bin/python3.11

while the original value was:

_=/usr/bin/env

Then this _ value alters the sys.path that Pyton uses in some way.

Is this behavior documented?

How to prevent _ from being altered when child Python processes are launched?

[picnixz]

For bash, the _ environment variable is documented as follows:

At shell startup, set to the absolute pathname used to invoke the shell or shell script being executed as passed in the environment or argument list. Subsequently, expands to the last argument to the previous command, after expansion. Also set to the full pathname used to invoke each command executed and placed in the environment exported to that command. When checking mail, this parameter holds the name of the mail file.

It's not modified by Python but by the underlying shell. See https://askubuntu.com/questions/1198935/what-is-the-purpose-of-the-special-parameter-single-underscore-in-environm.

[yurivict]

Also: why does _ alter sys.path that Python defaults to?
I am observing that sys.path becomes different when only the _ environment variable is different.

[picnixz]

Do you have some specific reproducer where we can see the behaviour you have vs the one you expect please? I would advise first asking on https://discuss.python.org/c/help.

[yurivict]

Never mind.