[Tox Support] Tox Wants to Recreate 2.7 Environment When Active, but Not 3.6

[nurupo]

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---
Regards,
nurupo

On 2019-01-14 18:58, Dan Lidral-Porter wrote:
> Hey Everybody,
> 
> I’ve run into a strange situation where Tox wants to recreate a Python
> 2.7 virtual environment whenever Tox is run with that environment
> active, using that environment’s own Python interpreter (which fails
> for obvious reasons). Curiously, this is not the case for the Python
> 3.6 environment when it is active, even though both of the
> environments’ Python interpreters have different MD5 sums than the
> system’s corresponding interpreter.
> 
> I’ve attached a minimal tox.ini file that reproduces my behavior. I am
> on OS X 10.13.6 with Python 2.7.15 and Python 3.6.5 installed with
> Homebrew. After the environments have been set up, I can then activate
> the Python 3.6 environment (named 'env') and re-run tox with no
> problems. Tox reuses the existing virtual environment so my command is
> quickly and successfully rerun. But if I activate the Python 2.7
> environment 'py27-env', tox tries to recreate py27-env using that
> environment's own interpreter, which — apart from being unnecessary —
> fails:
> 
> ```
> $ tox -ve py27-env
> using tox.ini: /Users/Daniel/src/scratch/tox-and-venvs/tox.ini
> using tox-3.7.0 from 
> /usr/local/lib/python3.6/site-packages/tox/__init__.py
> py27-env cannot reuse: attr base_resolved_python_md5
> 'bcfb5e550c2f501eb867a8aad7422ab7'!='c542cd220de26a93bf578d050a8926ec'
> py27-env recreate: /Users/Daniel/src/scratch/tox-and-venvs/py27-env
>   /Users/Daniel/src/scratch/tox-and-venvs$
> /usr/local/opt/python/bin/python3.6 -m virtualenv --python
> /Users/Daniel/src/scratch/tox-and-venvs/py27-env/bin/python2.7
> py27-env
> >/Users/Daniel/src/scratch/tox-and-venvs/py27-env/log/py27-env-0.log
> ERROR: invocation failed (exit code 3), logfile:
> /Users/Daniel/src/scratch/tox-and-venvs/py27-env/log/py27-env-0.log
> ERROR: actionid: py27-env
> msg: getenv
> cmdargs: '/usr/local/opt/python/bin/python3.6 -m virtualenv --python
> /Users/Daniel/src/scratch/tox-and-venvs/py27-env/bin/python2.7
> py27-env'
> 
> The path
> /Users/Daniel/src/scratch/tox-and-venvs/py27-env/bin/python2.7 (from
> --python=/Users/Daniel/src/scratch/tox-and-venvs/py27-env/bin/python2.7)
> does not exist
> 
> ERROR: Error creating virtualenv. Note that some special characters
> (e.g. ':' and unicode symbols) in paths are not supported by
> virtualenv. Error details:
> InvocationError('/usr/local/opt/python/bin/python3.6 -m virtualenv
> --python
> /Users/Daniel/src/scratch/tox-and-venvs/py27-env/bin/python2.7
> py27-env (see
> /Users/Daniel/src/scratch/tox-and-venvs/py27-env/log/py27-env-0.log)',
> 3)
> ```
> 
> I noticed that the change in the MD5 sum appears to have triggered the
> recreation. I confirmed that the virtual environment's python 2.7 and
> the system's python 2.7 do indeed have those two different MD5 sums
> that are listed in tox's output. Here is the part I don't understand:
> the MD5 sums for the other virtual environment's python 3.6 and the
> system's python 3.6 also differ, but when the 3.6 environment is
> active, tox doesn't try to recreate it! The system's python 3.6 has an
> MD5 sum of 631e2862c29aaf84e07aece6bba1f0de, but the virtual
> environment's is ecda41b60670d580a842d27d937ce8b6.
> 
> Why is it that tox tolerates the difference in MD5 sums for the 3.6
> environment, but not for the 2.7 one? My hope is that I'll be able to
> have tox ignore the different MD5 sums in the 2.7 environment as well,
> as the current behavior is breaking the development workflow for our
> data scientists because they cannot use tox to run tests when their
> 2.7 environment is active.
> 
> Thank you for your time.
> 
> Respecfully,
> 
> Dan Lidral-Porter | Data Scientist Sr
> 121 SW Salmon St., Suite 750, Portland, OR 97204
> cylance.com
> 
> -------------------------------------------------------------------------------
> 
> PS: contents of attached tox.ini file (in case attachment is removed):
> 
> [tox]
> envlist = env,py27-env
> skipsdist = True
> 
> [testenv]
> commands = python -c 'print("Hello, World!")'
> 
> [testenv:env]
> envdir = env
> basepython = python3.6
> 
> [testenv:py27-env]
> envdir = py27-env
> basepython = python2.7
> 
> 
> 
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