Pythong virtual envrionment setup

python virtual_env

# script for setting up pip and virtualenv on Ubuntu 16.04 
# Details can be found below 

#!/usr/bin/env bash

sudo apt-get install virtualenv python3-pip -y 
pip3 install --upgrade pip

# Installs virtualenvwrapper in  ~/.local/bin/
sudo pip3 install --user virtualenvwrapper

# (preferred)
# Installs virtualenvwrapper in  /usr/bin/ 
sudo pip3 install virtualenvwrapper

if `grep -q "source ~/.local/bin/virtualenvwrapper_lazy.sh" ~/.bashrc`;
then 
	echo "Virtual environment already exporte in ~/.bashrc file"
else 
cat << EOF >> ~/.bashrc

# Virtual env 
export WORKON_HOME=$HOME/.virtualenvs
export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3        # Set python version
export VIRTUALENVWRAPPER_SCRIPT=~/.local/bin/virtualenvwrapper.sh
source ~/.local/bin/virtualenvwrapper_lazy.sh

EOF


# If while creating virtualenv the following meesage appears which means python cannot load virtualenvwrapper module
# "/usr/bin/python: No module named virtualenvwrapper"
# then verify that $VIRTUALENVWRAPPER_PYTHON point to the right version of python for which virtualenvwrapper is installed

# For python3 it should be
# $ ls -l $VIRTUALENVWRAPPER_PYTHON
# lrwxrwxrwx 1 root root 9 Mär 20  2018 /usr/bin/python3 -> python3.5


fi
# the source command doesn't start a new shell instance but uses the current shell so the changes remain. 
source ~/.bashrc
exec bash

#################### END of Script   #####################################


# Efficiently manage virtual environment
# source : https://virtualenvwrapper.readthedocs.io/en/latest/
           http://askubuntu.com/questions/244641/how-to-set-up-and-use-a-virtual-python-environment-in-ubuntu
#          http://docs.python-guide.org/en/latest/dev/virtualenvs/
#
#
# Install virtualenv
    sudo apt-get install virtualenv (Ubuntu 16.04 or above)

    - Check version
        virtualenv --version

# First install pip and then use pip to install virtualenvwrapper
# so that virtualenvwrapper will be autometically install for that python vertion as pip

# Install pip for python3
    sudo apt-get -y install python3-pip
    pip3 install --upgrade pip

    - Check pip version
        pip3 --version

# Install virtualevnwrapper
    Because we want to avoid "sudo pip" we install virtualenvwrapper locally
    (by default under ~/.local) with:
    sudo pip3 install --user virtualenvwrapper


# Do the following steps to set virtualenvwrapper for lazy landing
    Source- http://virtualenvwrapper.readthedocs.io/en/latest/install.html#lazy-loading

export WORKON_HOME=$HOME/.virtualenvs
export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3        # Set python version
export VIRTUALENVWRAPPER_SCRIPT=~/.local/bin/virtualenvwrapper.sh
source ~/.local/bin/virtualenvwrapper_lazy.sh


# Let's Create a virtualenv
      mkvirtualenv test			(If this command hangs check "ls -l $VIRTUALENVWRAPPER_PYTHON" or change shell)
      mkvirtualenv test -p python3        # For python3 virtual environment
      # Work on the new virtual environment
      workon test
      # Deactivate running virtual environment
      deactive
      # Delete the environment
      rmvirtualenv test

# Save and use the packages in a virtual environment
      pip3 freeze > requirements.txt

# To load all the packages from requirements.txt
      pip install -r requirements.txt



#############################################################################################
#############################             Errors          ###################################
#############################################################################################
# If sourcing .bashrc gives "bash: /usr/share/virtualenvwrapper/virtualenvwrapper_lazy.sh: No such file or directory"
    - Uninstall virtualenvwrapper and remove the following file
        sudo rm /etc/bash_completion.d/virtualenvwrapper