How to create a Python 3.5 virtual environment with Python 2.7?

Question

My system is running CentOS 6. I do not have admin access, so sudo is not available. I have Python 2.7.3 available, along with pip and virtualenv. I was hoping that I could use these to set up a new virtual environment in which to install & run Python 3.5 or above.

I tried the method described here: Using Python 3 in virtualenv

But got this error:

$ virtualenv -p python3 venv
The path python3 (from --python=python3) does not exist

My system also has a Python 3.4 module installed, so I tried that, however virtualenv does not seem to work there:

$ module load python/3.4.3
$ virtualenv -p python3 venv
-bash: virtualenv: command not found

This appears to make sense since virtualenv is only installed for Python 2.7:

$ module unload python
$ module load python/2.7
$ which virtualenv
/local/apps/python/2.7.3/bin/virtualenv

So, the next logical step would seem to be installing virtualenv for my Python 3... but this does not work either:

$ pip3 install virtualenv
Traceback (most recent call last):
  File "/local/apps/python/3.4.3/bin/pip3", line 7, in <module>
    from pip import main
ImportError: cannot import name 'main'

also

$ pip3 install --user virtualenv
Traceback (most recent call last):
  File "/local/apps/python/3.4.3/bin/pip3", line 7, in <module>
    from pip import main
ImportError: cannot import name 'main'

I started Google'ing this new error message, but did not see anything that seemed relevant for this situation. Any ideas? Even if I could get virtualenv installed on my Python 3.4 module, would I still be unable to upgrade it to Python 3.5+?

To round things out, I also tried to compile my own Python 3.6 from source, but that does not work either:

Python-3.6.0$ make install
if test "no-framework" = "no-framework" ; then \
        /usr/bin/install -c python /usr/local/bin/python3.6m; \
    else \
        /usr/bin/install -c -s Mac/pythonw /usr/local/bin/python3.6m; \
    fi
/usr/bin/install: cannot create regular file `/usr/local/bin/python3.6m': Permission denied
make: *** [altbininstall] Error 1

more background info:

$ which pip3
/local/apps/python/3.4.3/bin/pip3

$ which python
/local/apps/python/3.4.3/bin/python

Answer 1

You can download miniconda or Anaconda. It does not require superuser privileges because it installs in your home directory. After you install you can create new environments like this:

conda create -n py35 python=3.5

Then you can switch to the new environment:

source activate py35