模块导入前需要Python命令行导入环境变量

Question

I use a module that has a default location to save files:

import foo # default directory is used to save files 

The module allows the use of an environment variable to change this location:

import os
os.environ['foo_path'] = "my/dir/path"
import foo # files now save in my/dir/path

If I import the module first, however, changing the environment variable does not help:

import os
import foo
os.environ['foo_path'] = "my/dir/path" #No effect, files saved in default location

My problem is the following : I want to be able to run my module via command line, and I want to allow the user to pass a path to set os.environ['foo_path'] .

I am using the click module to pass some arguments, and thought about using it to get the path from the command line. Ignoring the other arguments, this looks like this:

import click
import os

@click.command()
@click.option('--foo_path', default=None, help='dirpath to use instead of default', type=str)
def import_foo(foo_path):
    if foo_path:
        os.environ['foo_path'] = "my/dir/path" #Correctly changes the dirpath 
    import foo

This works , though the import in a function is a bit annoying.

However, if foo is somehow imported before, the approach does not work. Imagine I need to import another module bar that also imports foo :

import click
import bar # which imports foo
import os

@click.command()
@click.option('--foo_path', default=None, help='dirpath to use instead of default', type=str)
def import_foo(foo_path):
    if foo_path:
        os.environ['foo_path'] = "my/dir/path" #No effect, since foo already imported   
    import foo # not executed, since foo already imported by bar

Does anyone have a suggestion for passing environment required in module imports?

Answer 1

The environment in which you execute your script usually provides a way to set the value of an environment variable. For example, from the POSIX shell, you can simply prefix your Python command with an assignment that only applies to the new process's environment, rather than the current shell environment:

foo_path=/my/dir/path python script.py

If you plan on running the script multiple times, you can export the variable, so that each run inherits the value from the shell.

export foo_path=/my/dir/path
# Each of the following will see foo_path in its environment.
python script.py
python script.py
python script.py

Answer 2

Why do you need to save the location as an environment variable? Could you instead use sys.argv?

Test.py:

import sys

target_fp = sys.argv[1]
print('target_fp: ', target_fp)

Bash

python test.py 'example/path/to/file'
# ('target_fp: ', 'example/path/to/file')