For Python-3 try removing virtual environment files. And resetting it up.
rm -rf venv
virtualenv -p /usr/bin/python3 venv/
source venv/bin/activate
pip install -r requirements.txt
https://wiki.ubuntu.com/XenialXerus/ReleaseNotes#Python_3
edit fo
For Windows10 User.
I was using python3.4 on Windows10. I installed python3.5. I couldn’t find PYTHONPATH, PYTHONHOME env variable. If I command python in CMD console, It kept using python3.4. I deleted python3.4. Whenever I command python in CMD console, it starts showing an error like below.
Fatal Python error: Py_Initialize: Unable to get the locale encoding
ImportError: No module named ‘encodings’
I searched to figure out my problem. Solution was simple. When you install python3.5, you can custom install and check Add Python to environment variables in Advanced Options.
I just leave here for case that someone have similar issues visit here so that they don’t waste their precious time much to figure out.