Using Python 3 in virtualenv

Question

Using virtualenv, I run my projects with the default version of Python (2.7). On one project, I need to use Python 3.4.

I used brew install python3 to install it on my Mac. Now, how do I create a virtualenv that uses the new version?

e.g. sudo virtualenv envPython3

If I try:

virtualenv -p python3 test

I get:

Running virtualenv with interpreter /usr/local/bin/python3
Using base prefix '/usr/local/Cellar/python3/3.4.0_1/Frameworks/Python.framework/Versions/3.4'
New python executable in test/bin/python3.4
Also creating executable in test/bin/python
Failed to import the site module
Traceback (most recent call last):
  File "/Users/user/Documents/workspace/test/test/bin/../lib/python3.4/site.py", line 67, in <module>
    import os
  File "/Users/user/Documents/workspace/test/test/bin/../lib/python3.4/os.py", line 634, in <module>
    from _collections_abc import MutableMapping
ImportError: No module named '_collections_abc'
ERROR: The executable test/bin/python3.4 is not functioning
ERROR: It thinks sys.prefix is '/Users/user/Documents/workspace/test' (should be '/Users/user/Documents/workspace/test/test')
ERROR: virtualenv is not compatible with this system or executable

Answer 1

simply run

virtualenv -p python3 envname

Update after OP's edit:

There was a bug in the OP's version of virtualenv, as described here. The problem was fixed by running:

pip install --upgrade virtualenv

Answer 2

I'v tried pyenv and it's very handy for switching python versions (global, local in folder or in the virtualenv):

brew install pyenv

then install Python version you want:

pyenv install 3.5.0

and simply create virtualenv with path to needed interpreter version:

virtualenv -p /Users/johnny/.pyenv/versions/3.5.0/bin/python3.5 myenv

That's it, check the version:

. ./myenv/bin/activate && python -V

There are also plugin for pyenv pyenv-virtualenv but it didn't work for me somehow.

Answer 3

Python 3 has a built-in support for virtual environments - venv. It might be better to use that instead. Referring to the docs:

Creation of virtual environments is done by executing the pyvenv script:

pyvenv /path/to/new/virtual/environment

Update for Python 3.6 and newer:

As pawciobiel correctly comments, pyvenv is deprecated as of Python 3.6 and the new way is:

python3 -m venv /path/to/new/virtual/environment