It is a built-in plugin in TeXmacs. If you need to customize it, please install it under the $TEXMACS_HOME_PATH:

# For GNU/Linux or macOS:
git clone [email protected]:texmacs/python.git $HOME/.TeXmacs/plugins/python

# For Windows:
git clone [email protected]:texmacs/python.git %APPDATA%\TeXmacs\plugins\python

Install the Python plugin to $TEXMACS_HOME_PATH/plugins and then change the python launcher in $TEXMACS_HOME_PATH/plugins/python/progs/init-python.scm.

If you have permissions for $TEXMACS_PATH/plugins/python/progs/init-python.scm, you may also change the system one.

Here is the detailed example of changing the python command:

(define (python-command) "python3")

By default, we use python3. To use a specific python version, just change the return value of the (python-commond) function.

(define (python-command) "/path/to/python")