tox Invocation failed for Python 3

Question

tox runs my Python 2.7 tests, but fails for Python 3.4. It gives an "Invocation failed" message. Excerpts:

py34 create: /home/josh/code/ezoutlet/.tox/py34
ERROR: invocation failed (exit code 1), logfile: /home/josh/code/ezoutlet/.tox/py34/log/py34-0.log
ERROR: actionid: py34
msg: getenv
cmdargs: ['/usr/bin/python', '-m', 'virtualenv', '--python', '/usr/bin/python3.4', 'py34']

And later

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/virtualenv.py", line 8, in <module>
    import base64
  File "/usr/lib/python3.4/base64.py", line 9, in <module>
    import re
  File "/usr/lib/python3.4/re.py", line 336, in <module>
    import copyreg
  File "/usr/local/lib/python2.7/dist-packages/copyreg/__init__.py", line 7, in <module>
    raise ImportError('This package should not be accessible on Python 3. '
ImportError: This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 53, in apport_excepthook
    if not enabled():
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 24, in enabled
    import re
  File "/usr/lib/python3.4/re.py", line 336, in <module>
    import copyreg
  File "/usr/local/lib/python2.7/dist-packages/copyreg/__init__.py", line 7, in <module>
    raise ImportError('This package should not be accessible on Python 3. '
ImportError: This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.

Original exception was:
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/virtualenv.py", line 8, in <module>
    import base64
  File "/usr/lib/python3.4/base64.py", line 9, in <module>
    import re
  File "/usr/lib/python3.4/re.py", line 336, in <module>
    import copyreg
  File "/usr/local/lib/python2.7/dist-packages/copyreg/__init__.py", line 7, in <module>
    raise ImportError('This package should not be accessible on Python 3. '
ImportError: This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.
Running virtualenv with interpreter /usr/bin/python3.4

ERROR: InvocationError: /usr/bin/python -m virtualenv --python /usr/bin/python3.4 py34 (see /home/josh/code/ezoutlet/.tox/py34/log/py34-0.log)

Answer 1

You need to look at the details of the error message. Notice the command that failed (from the first excerpt):

cmdargs: ['/usr/bin/python', '-m', 'virtualenv', '--python', '/usr/bin/python3.4', 'py34']

You can run this manually with:

/usr/bin/python -m virtualenv --python /usr/bin/python3.4 py34

Assuming you see the same error, your issue is with virtualenv rather than tox.

I reviewed the virtualenv help page and it seems like this should work. Faced with a possible bug, a good first step is to upgrade Python, virtualenv, or other libraries.

In my case, upgrading virtualenv was the solution:

pip install --upgrade virtualenv

Interestingly, this solution worked on both Windows and Linux. Most likely, there was a bug fix between when I got virtualenv and the latest release.