Installing `pymbar` from conda forcing a downgrade of Python 3.7 → 3.6

Installing pymbar from omnia via conda is trying to downgrade python (and a bunch of other packages). I’m not sure this is the intended effect (I can’t see anything in the repository pinning python=3.6 or python<3.7).

Briefly, I had an environment with pymbar installed, upgraded ambertools from 18 to 19 and python from 3.6.x to 3.7.3. I then lost the ability to import pymbar. I thought this was probably removed accidentally during whatever magic conda uses for conflict management, but trying to reinstall pymbar using the same command will downgrade ~20 packages, including python.

(paprika-dev) /m/d/d/p/pAPRika-dev ❯❯❯ conda install -c omnia pymbar                                             ✘ 2 openmm-2
Collecting package metadata: done
Solving environment: done

## Package Plan ##

  environment location: /home/davids4/data/anaconda3/envs/paprika-dev

  added / updated specs:
    - pymbar


The following packages will be downloaded:

    package                    |            build
    ---------------------------|-----------------
    coverage-4.3.4             |           py36_0         226 KB  omnia
    ------------------------------------------------------------
                                           Total:         226 KB

The following NEW packages will be INSTALLED:

  pymbar             omnia/linux-64::pymbar-3.0.1.beta0-np111py36_0


[snip]
The following packages will be DOWNGRADED:
[snip]
  python                                   3.7.3-h0371630_0 --> 3.6.8-h0371630_0

[Lnaden]

Right. If you use another conda install or similar command with different -c ... settings, it resolves only for that command and makes changes to the environment to solve that specific call. Its why we say for all omnia packages to also include conda-forge as a higher priority channel to help reduce those oddities. If you are having issues with resolution, try doing everything in 1 line carefully considering the channel priority.

[slochower]

Yup