You can install the free system virtualization tools that are mentioned in this chapter from the following sites:

• Vagrant: https://www.vagrantup.com
• Docker: https://www.docker.com
• VirtualBox: https://www.virtualbox.org/

The following are the Python packages that are mentioned in this chapter that you can download from PyPI:

• poetry
• flask
• wait-for-it
• watchdog
• ipython
• ipdb

Information on how to install packages is included in the Installing Python packages using pip section.

The code files for this chapter can be found at https://github.com/PacktPublishing/Expert-Python-Programming-Fourth-Edition/tree/main/Chapter%202.

The core of Python's packaging ecosystem is the Python Packaging Index. PyPI is a vast public repository of (mostly) free-to-use Python projects that at the time of writing hosts almost three and a half million distributions of more than 250,000 packages. That's not the biggest number among all package repositories (npm surpassed a million packages in 2019) but it still places Python among the leaders of packaging ecosystems.

Such a large ecosystem of packages doesn't come without a price. Modern applications are often built using multiple packages from PyPI that often have their own dependencies. Those dependencies can also have their own dependencies. In large applications, such dependency chains can go on and on. Add the fact that some packages may require specific versions of other packages and you may quickly run into dependency hell—a situation where it is almost impossible to resolve conflicting version requirements...

When you use pip to install a new package from PyPI, it will be installed into one of the available site-packages directories. The exact location of site-packages directories is specific to the operating system. You can inspect paths where Python will be searching for modules and packages by using the site module as a command as follows:

$ python3 -m site

The following is an example output of running python3 -m site on macOS:

sys.path = [
    '/Users/swistakm',
    '/Library/Frameworks/Python.framework/Versions/3.9/lib/python39.zip',
    '/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9',
    '/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/lib-dynload',
    '/Users/swistakm/Library/Python/3.9/lib/python/site-packages',
    '/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages',
]
USER_BASE: '/Users/swistakm/Library...

Python has built-in support for creating virtual environments. It comes in the form of a venv module that can be invoked directly from your system shell. To create a new virtual environment, simply use the following command:

$ python3.9 -m venv <env-name>

Here, env-name should be replaced with the desired name for the new environment (it can also be an absolute path). Note how we used the python3.9 command instead of plain python3. That's because depending on the environment, python3 may be linked to different interpreter versions and it is always better to be very explicit about the Python version when creating new virtual environments. The python3.9 -m venv commands will create a new env-name directory in the current working directory path. Inside, it will contain a few sub-directories:

• bin/: This is where the new Python executable and scripts/executables provided by other packages are...

The key enabler to the rapid iteration of software implementation is the reuse of existing software components. Don't repeat yourself—this is a common mantra of many programmers. Using other packages and modules to include them in the codebase is only a part of that mindset. What can also be considered as reused components are binary libraries, databases, system services, third-party APIs, and so on. Even whole operating systems should be considered as a component that is being reused.

The backend services of web-based applications are a great example of how complex such applications can be. The simplest software stack usually consists of a few layers. Consider some imaginary application that allows you to store some information of its users and exposes it to the internet over the HTTP protocol. It could have at least the three following layers (starting from the lowest):

• A database or other kind of...

Almost every open-source Python package that has been released on PyPI is a kind of productivity booster—it provides ready-to-use solutions to some problem. That way we don't have to reinvent the wheel all the time. Some could also say that Python itself is all about productivity. Almost everything in this language and the community surrounding it seems to be designed to make software development as productive as possible.

This creates a positive feedback loop. Since writing code with Python is fun and easy, a lot of programmers use their free time to create tools that make it even easier and more fun. And this fact will be used here as a basis for a very subjective and non-scientific definition of a productivity tool—a piece of software that makes development easier and more fun.

By nature, productivity tools focus mainly on certain elements of the development process, such as testing, debugging, and managing packages, and are...

This chapter was all about development environments for Python programmers. We've discussed the importance of environment isolation for Python projects. You've learned two different levels of environment isolation (application-level and system-level), and multiple tools that allow you to create them in a consistent and repeatable manner. We've also discussed some essential topics for managing Python dependencies in your projects. This chapter ended with a review of a few tools that improve the ways in which you can experiment with Python or debug your programs and work effectively.

Once you have all of these tools in your tool belt, you are well-prepared for the next few chapters, where we will discuss multiple features of modern Python syntax. You're probably already hungry for Python code so we will start with a quick overview of the new things that were included in Python over the last few releases.

If you're quite up to date with what&apos...