Managing Python Virtual Environments

In this chapter, you will get to know what a virtual environment in Python is, how to create and use a virtual environment for building a Python application.

When you install Python software on your computer, it is available for use from anywhere in the filesystem. This is a system-wide installation.

While developing an application in Python, one or more libraries may be required to be installed using the pip utility (e.g., pip3 install somelib). Moreover, an application (let us say App1) may require a particular version of the library, say somelib 1.0. At the same time another Python application (for example App2) may require newer version of same library say somelib 2.0. Hence by installing a new version, the functionality of App1 may be compromised because of conflict between two different versions of same library.

This conflict can be avoided by providing two isolated environments of Python in the samemachine. These are called virtual environment. A virtual environment is a separatedirectory structure containing isolated installation having a local copy of Python interpreter, standard library and other modules.

The following figure shows the purpose of advantage of using virtual environment. Using the global Python installation, more than one virtual environments are created, each having different version of the same library, so that conflict is avoided.

This functionality is supported by venv module in standard Python distribution. Use following commands to create a new virtual environment.

Here, myvenv is the folder in which a new Python virtual environment will be created showing following directory structure −

The utilities for activating and deactivating the virtual environment as well as the local copy of Python interpreter will be placed in the scripts folder.

To enable this new virtual environment, execute activate.bat in Scripts folder.

Note the name of the virtual environment in the parentheses. The Scripts folder contains a local copy of Python interpreter. You can start a Python session in this virtual environment.

To confirm whether this Python session is in virtual environment check the sys.path.

The scripts folder of this virtual environment also contains pip utilities. If you install a package from PyPI, that package will be active only in current virtual environment. To deactivate this environment, run deactivate.bat.

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