RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.6'

[benjeffery]

Over at tskit-dev/tskit#498 a user has reported this error:

An unexpected error has occurred: CalledProcessError: command: ('/usr/bin/python3', '-mvirtualenv', '/home/peter/.cache/pre-commit/repoeh3i9c_u/py_env-python3.6', '-p', 'python3.6')
return code: 1
expected return code: 0
stdout:
    RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.6'

Is this related to pypa/virtualenv#1515 ?

[benjeffery]

Config at https://github.com/tskit-dev/tskit/blob/master/.pre-commit-config.yaml
Version 2.2.0

Seems adding language_version: python3.7 to the black config fixed this, as they didn't have python 3.6 on their system, but might that break people who have 3.6 only?

[asottile]

this probably means they don't have python3.6 -- probably best to do language_version: python3 and then that should work for most that have a modern-enough python

[benjeffery]

Brill - thanks for that!

[asottile]

@gaborbernat -- just a data point, I think the old error message was easier to understand here:

$ virtualenv -p python3.6 vvv
The path python3.6 (from --python=python3.6) does not exist

vs

$ virtualenv -p python3.6 vvv
RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.6'

[gaborbernat]

Well, in theory it's more accurate to say could not be found opposed to does not exists; because the executable might still be available on the machine, we could just not discover it because e.g. it's no on the PATH.

[asottile]

yeah, perhaps just some wording can be rearranged, maybe something like this?

`python3.6` (from --python=python3.6) was not found while attempting Builtin discovery.

[guilleijo]

For anyone still having this problem, following @asottile recommendation of adding language_version: python3 in the conflicting repos works. In case that you need to add it in all repos and don't want to repeat the same line multiple times, you can add a global default.

default_language_version:
    python: python3

You can use a more specific version, in my case I'm using python: python3.7.