--proxy should override environment variables

[meiswjn]

Description

Hey,

When specifying proxies in both the environment variables (http_proxy, ...) and the --proxy parameter, the environment variables seem to take precedence.
Since --proxy is more explicit, it should be used whenever specified (even over pip config).

While it is possible to temporarily change the environment variables, it is much more work:

export http_proxy="<alternate_proxy>"
export https_proxy="<alternate_proxy>"
pip install -r requirements.txt
export http_proxy="<original_proxy>"
export https_proxy="<original_proxy>"

vs.

pip --proxy=<alternate_proxy> -r requirements.txt

Expected behavior

No response

pip version

20.0.2

Python version

3.8

OS

Ubuntu

How to Reproduce

1. Define environment variables HTTP_PROXY, HTTPS_PROXY, http_proxy, https_proxy
2. Install a package with --proxy= and specify a different proxy

Output

No response

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

I think I agree. I don’t use proxies (like ever…), but it makes sense for an argument to have higher precedence over environment variables of the same functionality. Would you be interested in sending in a pull request?

[meiswjn]

Sure, done. Let me know if changes are required.