Python plugin --classic snap conflicts with system python

[Casper]

Using a published `confinement: classic` snap using `plugin: python`, multiple people seem to have reported the snap trying to use/`import` host libraries rather than the dependencies installed during the snap plugin's build stage.

Errors:

https://github.com/iterative/dvc/issues/3514

Snapcraft config:

https://github.com/iterative/dvc/blob/master/snap/snapcraft.yaml

[Sergio Schvezov (sergiusens)]

This seems to be a bug in the interpreter that dvc is running itself. In command there is bin/dvc, and bin/dvc is just a script calling python from $PATH, and as such, the "python" found in PATH is python from the system.

[Casper (casper-dcl)]

Thanks for looking into this - however not sure if that's the problem.

A `plugin: python` snap should not be trying to use the system's `PATH` over its own internal python interpreter. Also:

$ python --version
Python 2.7.15
$ python -m dvc version
/home/user/miniconda/bin/python: No module named dvc
$ which dvc
/snap/bin/dvc
$ dvc version
DVC version: 1.0.0a5
Python version: 3.6.9
Platform: Linux-4.15.0-58-generic-x86_64-with-Ubuntu-16.04-xenial
Binary: False
Package: snap
Supported remotes: azure, gdrive, gs, hdfs, http, https, s3, ssh, oss
$ echo $PATH
...:/home/user/miniconda/bin:...:/snap/bin:...

clearly indeed the `snap` is picking up its own internal python and not the system's python even though the user's `PATH` has the system python first.