Env var for using specific Python version

[TheLastProject]

It'd be great to have something like CONDA_PYTHON_VERSION or so to be able to explicitly request for example 3.6 instead of 3.7. In my case, one of my dependencies doesn't build on 3.7 yet, and conda upgraded from 3.6 to 3.7, so now my build is broken with seemingly nothing I can do.

[TheAssassin]

Good idea.

Right now, we're downloading some "miniconda v3 latest" script. Any idea how we could request a version explicitly?

[TheAssassin]

Miniconda's version script differs from Python's. See https://repo.continuum.io/miniconda/.

[TheLastProject]

You can use conda create -n envname anaconda python=3.6 and instead of using activate use activate envname. Would probably only be a very small change actually.

[TheLastProject]

Actually, I think anaconda shouldn't be in that command. Documentation is a bit weird.

[TheAssassin]

I see. I will test a bit.

Shall we recognize and support Python 2 as well?

[TheLastProject]

Well, that'll make things slightly more complex I suppose, but it's a logical next step letting people use 2 for "latest python 2"

[TheAssassin]

My idea was to download the Python 2 miniconda script if the version begins with 2, and if it's exactly 2 just use the latest, otherwise install a version explicitly.

[TheLastProject]

Sounds good yeah

[TheAssassin]

Let's first focus on the Python 3 aspects.

[TheAssassin]

Tested adding a call like conda install python=<version>. This doesn't "just work" with older versions like 3.4:

Warning: 'conda-forge' already in 'channels' list, moving to the top
Solving environment: failed

UnsatisfiableError: The following specifications were found to be in conflict:
  - conda[version='>=4.5.11'] -> pycosat[version='>=0.6.3'] -> python[version='>=3.6,<3.7.0a0']
  - python=3.4
Use "conda info <package>" to see the dependencies for each package.

I don't know how to map "conda script version" to "works for python version". Ideas welcome.

[TheLastProject]

My idea was more based around #5.