Creating a virtualenv for each project will simplify your life, avoiding version and package conflicts across multiple projects. When you are ready to publish, creating a requirements.txt allows other users to replicate your app or script output (you will thank yourself later).

How to install virtualenv for python projects:

Install pip first

sudo apt-get install python3-pip

Then install virtualenv using pip3

sudo pip3 install virtualenv 

Now create a virtual environment

virtualenv venv 

you can use any name instead of venv

You can also use a Python interpreter of your choice

virtualenv -p /usr/bin/python2.7 venv

Active your virtual environment:

source venv/bin/activate

Using fish shell:

source venv/bin/activate.fish

To deactivate:

deactivate

Create virtualenv using Python3

virtualenv -p python3 myenv

Instead of using virtualenv you can use this command in Python3

python3 -m venv myenv

Once your project is ready to publish, let’s create an requirements.txt:

write the file

pip freeze > requirements.txt

show the file’s contents

cat requirements.txt

When starting from refresh virtualenv or new pc, install requirements.txt to replicate dependancies:

For virtualenv to install all files, cd to the directory where requirements.txt is located

activate your virtualenv

source venv/bin/activate ### run 
pip install -r requirements.txt