How to change python version used by python-green

Question

I have both Python 2.7 and 3.3 installed in my box. How would I change python-green configuration to use one or the other without changing /usr/bin/python symbolic link?

Answer 1

Try venv. This creates a virtual environment where all scripts use a particular python version by default.

pip install virtualenv
virutalenv -p <PATH_TO_PYTHON_3> <VENV_PATH>
source <VENV_PATH>/Scripts/activate

Once you activate venv,

install green
green <MODULE_TO_TEST>

To stop using this environment,

deactivate

Most packages, even the ones which support multiple Python versions, don't have run-time switches. So, you need to install green after you activate venv. Otherwise, the currently active (in your case, global) python version - lets assume 2.7 - calls its globally installed pip, which would install green for Python 2.7.

Answer 2

green can now be run directly as a module. To do this, use /path/to/python -m green

Answer 3

Using venv as Sharadh suggests is absolutely the best way to go about this.

Having said that, it can be useful to know that green actually installs three application binaries:

green
greenX
greenX.Y

Where X is the major version of python (2 or 3) and Y is the minor version of python. So lets say you install green under the "system" installation of Python 3.3 and then 3.4. The following would occur:

green    <- Points to green in 3.3
green3   <- Points to green in 3.3
green3.3 <- Points to green in 3.3
green    <- Overwrites the previous green, now points to 3.4
green3   <- Overwrites the previous green3, now points to 3.4
green3.4 <- Points to green in 3.4

So, in summary:

1. Use venv -- it's much more sane.
2. If you must use multiple "system" python versions, use greenX.Y in all your commands, and you'll always get the correct one.