How to work on a Python Project when modules versions needed are different? Use virtualenv

Gone are the days when you need to create a VM for working on a different set of tools.  People work on different projects which might need a special version of a module. (Or python itself) . The problem aggravates when  multiple users work on a single shared machine (Test environments or Build machines ) .Virtual Environments help solve problem . And its easy to use and share among fellow teammates.


Installation:

pip install virtualenv

Note: I am using 15.2.0 ver of vituralenv module and my system is Windows 10 64 bit.

(Windows OS) Creating a virtual environment:

virtualenv ProjectName

This will take some time . If you have only one installation of Python , then above step will use that Python version . Lets say you have two different python installations (2.7 and 3.4) . Then you can specify which python to be used to make this environment . For creating a version specific env, use this :

virtualenv -p C:\Python27\python.exe temp_project

Note :  My python executable file path is used as above to specify which python to be used.

After the VE has been created , you can see the below contents in that folder .

Now to activate the environment , browse to script folder inside the above temp_project folder. Type in command prompt:

Scripts\activate

Now you will see on you prompt, your virtaulenv name inside parenthesis. Example:

(temp_project) C:\User\temp_project

Now we can install all the modules that we need for our project using pip command. 

To deactivate,

Scripts\deactivate

You can generate a list of requirements from you installed modules:

pip freeze > requirements.txt

Other Important tips:

• If you need to install using a wheel file, you should copy the .whl file inside Lib\site-packages and then use "pip install filename.whl" . 
• It's a good practice to upgrade certain modules like (setuptools, pip, incremental) before you start installing other modules.        

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On Unix system , creating and activating a virtualenv has different approach

To create:

virtualenv -p /usr/bin/python3

Tip: Use "which python" or "which python3" to find the path of python.

To activate , type: 

source MyVirtualEnv/bin/activate

To deactivate:

deativate