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I am trying to create a new environment with Python 3.7 using Conda like:

conda create -n qnn python=3.7

I got following errors:

Collecting package metadata (current_repodata.json): done
Solving environment: failed with repodata from current_repodata.json, will retry with next repodata source.
Collecting package metadata (repodata.json): done
Solving environment: failed

PackagesNotFoundError: The following packages are not available from current channels:

  - python==3.7

Current channels:

  - https://conda.anaconda.org/conda-forge/osx-arm64
  - https://conda.anaconda.org/conda-forge/noarch

To search for alternate channels that may provide the conda package you're
looking for, navigate to

    https://anaconda.org

and use the search bar at the top of the page.

Why is Python 3.7 apparently unavailable?

System Details

This is on an Apple Silicon (osx-arm64) machine running macOS.

merv
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youngtackpark
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    What is your question? Have you used the suggested search option on anaconda.org or `conda search python` in the command line to see which versions are available? – FlyingTeller Dec 03 '21 at 09:30
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    support for arm64 is relatively new on conda-forge. I feel the problem is that you requested an older version of python and conda-forge does not support it. Moreover, I think as it is now this is a valid and clear question which does not merit closing. – cel Dec 03 '21 at 15:34

2 Answers2

61

No native builds available

Since Python 3.8 had been released for about a year when Apple Silicon hit the market, Python 3.7 builds for osx-arm64 were never part of the regular build matrix for Conda Forge.

Workaround: Emulate

Immediate alternatives for using 3.7 on Apple Silicon systems would be to emulate x86_64 with Rosetta or use a container system, e.g., Docker.

Creating osx-64 environments

Similar to what one does for running win-32 environments on x86_64 machines, one can create osx-64 environments like

## create empty environment
conda create -n py37

## activate
conda activate py37

## use x86_64 architecture channel(s)
conda config --env --set subdir osx-64

## install python, numpy, etc. (add more packages here...)
conda install python=3.7 numpy

⚠️ Important Note: Be sure to always activate this environment before installing packages. Otherwise, the default CONDA_SUBDIR value (osx-arm64) may be active and could result in mixing architectures in the same environment.

Note that MacOS will automatically recognize the architecture and run through Rosetta (once installed) - one need not do anything special.

YAML

With a YAML environment definition, one can use the CONDA_SUBDIR environment variable to temporarily set the platform while creating the environment. Again, one still should set the environment-specific subdir option immediately after creation.

## create environment from YAML
CONDA_SUBDIR=osx-64 conda env create -n py37 -f py37.yaml

## activate
conda activate py37

## use x86_64 architecture channel(s)
conda config --env --set subdir osx-64

Requesting native build

Longer term, you could try requesting that the python-feedstock include a 3.7 build for osx-arm64. However, 3.7.12 (Sept. 2021) was technically the final feature release, and it has now entered the maintenance-only phase (see PEP 537). Also, other packages that build Python-version-specific variants would not be built for osx-arm64, so even if one had python=3.7, the packages wouldn't be there (at least not through Conda). Basically, I wouldn't bet on anyone taking this up.

merv
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    Thanks! It worked! I used `conda config --env --set subdir osx-64` before `conda create -n demo python=3.7`. – shihs Jul 04 '22 at 12:58
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    @shihs that means subdir was set for another environment - that is not correct. It must be set for the intended target environment. You should unset it in the original environment it was set in. – merv Jul 04 '22 at 14:55
  • But why it could work? On the other hand, after the command `conda config --env --set subdir osx-64`, `python 3.7` shows in `conda search python` list. I thought this means python3.7 is available for the environment? – shihs Jul 05 '22 at 02:04
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    @shihs that sets the subdir for the current environment, and Conda still uses that configuration setting as long as it is active, despite running `conda create` for a new environment. The next time you try using `conda install` in the environment, Conda will try to installing everything as **osx-64**, whereas in the new environment it will default back to **osx-arm64**. – merv Jul 05 '22 at 16:31
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    This worked, but a critical step is to make sure you've installed Rosetta 2, especially before attempting to run `conda install ...`. You can do that with `softwareupdate --install-rosetta` https://support.apple.com/en-gb/HT211861 – Matt M Oct 18 '22 at 23:44
  • `conda config --env --set subdir osx-arm64` in case you need to switch back to ARM architecture. – George Shimanovsky May 07 '23 at 18:01
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Not sure if this is the best strategy, but running

CONDA_SUBDIR=osx-64 conda

worked for my use case.

sebpretzer
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