Python: Avoid version conflicts with Virtual Environments

# Virtual Environments ("virtualenvs") keep
# your project dependencies separated.
# They help you avoid version conflicts
# between packages and different versions
# of the Python runtime.

# Before creating & activating a virtualenv:
# `python` and `pip` map to the system
# version of the Python interpreter
# (e.g. Python 2.7)
$ which python
/usr/local/bin/python

# Let's create a fresh virtualenv using
# another version of Python (Python 3):
$ python3 -m venv ./venv

# A virtualenv is just a "Python
# environment in a folder":
$ ls ./venv
bin      include    lib      pyvenv.cfg

# Activating a virtualenv configures the
# current shell session to use the python
# (and pip) commands from the virtualenv
# folder instead of the global environment:
$ source ./venv/bin/activate

# Note how activating a virtualenv modifies
# your shell prompt with a little note
# showing the name of the virtualenv folder:
(venv) $ echo "wee!"

# With an active virtualenv, the `python`
# command maps to the interpreter binary
# *inside the active virtualenv*:
(venv) $ which python
/Users/dan/my-project/venv/bin/python3

# Installing new libraries and frameworks
# with `pip` now installs them *into the
# virtualenv sandbox*, leaving your global
# environment (and any other virtualenvs)
# completely unmodified:
(venv) $ pip install requests

# To get back to the global Python
# environment, run the following command:
(venv) $ deactivate

# (See how the prompt changed back
# to "normal" again?)
$ echo "yay!"

# Deactivating the virtualenv flipped the
# `python` and `pip` commands back to
# the global environment:
$ which python
/usr/local/bin/python

Python : What is Virtual Environment

Each project might need some set of dependencies with their specific version to work properly. Usually, we might have multiple projects running on different versions / packages. For example

  • some project on python2 others python 3
  • some project using pymongo2.7 others pymongo3.2

Normally, we have installed python 2.7, then we might not run python3 without upgrading to python3, however there is solution called virtual Environment which allows us to have an environment for specific required for each project and it is called as virtual environment. This can be installed using below command

$ [sudo] pip install virtualenv

The trick is to create separate folder for each project and activate virtual environment over there, that way requirements might not clash with each other. 

for example, i have 2 projects named make_money and spend_money wh

So I have to make 2 different directories and install virtual environment in them, I can run my project from any where, however the dependencies would be installed in that specific project. 

It is kind of similar to NPM for node, and pip is similar to maven in java

Helpful link : https://www.dabapps.com/blog/introduction-to-pip-and-virtualenv-python/