Managing dependencies and virtual environments

In this section, you will be able to identify how to manage dependencies and the execution environment with pip and virtualenv.

Managing dependencies in a Python project

If our project has dependencies with other libraries, the goal will be to have a file where we have such dependencies, so that our module is built and distributed as quickly as possible. For this function, we can create a file called requirements.txt, which contains all the dependencies the module requires.

To install all the dependencies, we can use the following command with the pip utility:

$ pip -r requirements.txt

Here, pip is the Python package and dependency manager and requirements.txt is the file where all the dependencies of the project are saved.

Install Python modules

Python has an active community of developers and users who develop both standard Python modules, as well as modules and packages developed by third parties. The Python Package Index, or PyPI (https://pypi.org), is the official software package repository for third-party applications in the Python programming language.

To install a new python Package, you have the following alternatives:

• Use the one that is packaged depending on the operating system and distribution you are using. For example, using apt-cache show <package>
• Install pip on your computer and, as a superuser, install the Python package that interests us. This solution can give us many problems, since we can break the dependencies between the versions of our Python packages installed on the system and some package may stop working.
• Use virtual environments: It is a mechanism that allows you to manage Python programs and packages without having administration permissions, that is, any user without privileges can have one or more “isolated spaces” where they can install different versions of Python programs and packages. To create the virtual environments, we can use the virtualenv program or the venv module.

Generating the requirements.txt file

We also have the ability to create the requirements.txt file from the project source code. For this task, we can use the pipreqs module, whose code can be downloaded from the GitHub repository at https://github.com/bndr/pipreqs.

In this way, the module can be installed either with the pip install pipreqs command or through the GitHub code repository using the python setup.py install command.

For more information about the module, you can refer to the official PyPI page https://pypi.org/project/pipreqs/.

To generate the requirements.txt file, you could execute the following command:

$ pipreqs <path_project>

Working with virtual environments

When operating with Python, it’s strongly recommended that you use virtual environments. A virtual environment provides a separate environment for installing Python modules and an isolated copy of the Python executable file and associated files.

You can have as many virtual environments as you need, which means that you can have multiple module configurations configured, and you can easily switch between them.

Configuring virtualenv

When you install a Python module on your local computer without having to use a virtual environment, you install it on the operating system globally. Typically, this installation requires a user root administrator, and the Python module is configured for each user and project.

The best approach at this point is to create a Python virtual environment if you need to work on many Python projects, or if you are working with several projects that are sharing some modules.

virtualenv is a Python module that enables you to build isolated, virtual environments. Essentially, you must create a folder that contains all the executable files and modules needed for a project. You can install virtualenv as follows:

1. Type in the following command:

   $ sudo pip install virtualenv
   

2. To create a new virtual environment, create a new folder and enter the folder from the command line:

   $ cd your_new_folder
   $ virtualenv name-of-virtual-environment
   $ source bin/activate
   

3. Once it is active, you will have a clean environment of modules and libraries, and you will have to download the dependencies of the project so that they are copied in this directory using the following command:

   (venv) > pip install -r requirements.txt
   

   Executing this command will initiate a folder with the name indicated in your current working directory with all the executable files of Python and the pip module, which allows you to install different packages in your virtual environment.

   IMPORTANT NOTE

   If you are working with Python 3.3+, virtualenv is included in stdlib. You can get an installation update for virtualenv in the Python documentation: https://docs.python.org/3/library/venv.html.

4. virtualenv is like a sandbox where all the dependencies of the project will be installed when you are working, and all modules and dependencies are kept separate. If users have the same version of Python installed on their machine, the same code will work in the virtual environment without requiring any changes.

Now that you know how to install your own virtual environment, let’s move on to review development environments for Python scripting, including Python IDLE and PyCharm.