Where is the mkvirtualenv --python command-line argument documented?

Question

I was taking a course on django and when creating a virtual environment, they used the following command:

mkvirtualenv envname --python=/usr/bin/python3.8

I've no idea what the additional arguments mean, and just wanted an explanation. Many thanks! Apologies if this is something simple - just starting out.

The shell (Bash or otherwise) simply executes the command line, using the first token as the command and the others as string arguments. So your question is actually, what does this option mean to the command `virtualenv`? — tripleee, Aug 29 '21 at 13:01
In general, you can find the documentation for each command and its options in its manual page. Many commands also support a `--help` option which typically displays a list of the supported options with a brief description of each. — tripleee, Aug 29 '21 at 13:03
Your question is not related to `bash` at all; `--python` is a parameter to `mkvirtualenv`. — Manfred, Aug 29 '21 at 13:03
@tripleee The `--python` parameter is not documented, as far as I can tell. — Dai, Aug 29 '21 at 13:03
@Dai - precisely, can't find any documentation for it, which is why I was hoping to find someone who knew it. Oh well :) — Selerium, Aug 29 '21 at 13:07

Dai · Accepted Answer · 2021-08-29T13:12:47.600

The mkvirtualenv command is a shell-script that usually lives at /usr/local/bin/virtualenvwrapper.sh.
The source-code for which can be found on GitHub.
In it, references to the --python command-line parameter can be found in the bash-function function mkvirtualenv {.
This is the relevant part ([...] denotes code I removed for readability): it loops over all provided command-line arguments:

function mkvirtualenv {
    [...]
    while [ $i $tst $# ]
    do
    a="${in_args[$i]}"
    case "$a" in
        [...]
        -p|--python)
            i=$(( $i + 1 ));
            interpreter="${in_args[$i]}";
            interpreter="$(virtualenvwrapper_absolutepath "$interpreter")";;
        [...]
    esac
    i=$(( $i + 1 ))
done

The above code handles the --python command-line argument.
The --python (double-dash) and -p (single-dash) arguments are treated as synonyms.
It's used to set the path to the actual Python interpreter/engine that your new virtual-environment will use.
This is needed because you can have multiple, different, and incompatible Python installs side-by-side on the same physical computer, but you need to select a single unambiguous (and correctly versioned) Python executable to run your Python programs.

Where is the mkvirtualenv --python command-line argument documented?

1 Answers1