What is a pyproject.toml file?

Are you wondering what a pyproject.toml file is used for? Then we have the answers you are looking for! In this article we go over everything you need to know to understand when you need to use a pyproject.toml file and exactly what a pyproject.toml file is used for. In addition to talking about what a pyproject.toml file is used for, we also give an example of how a pyproject.toml file should be structured. 

When is a pyproject.toml file used?

Before talking about what a pyproject.toml file is used for, it is first useful to understand when a pyproject.toml file should be used. A pyproject.toml file is a file that you should use if you are creating a Python package so that you can import your Python code and use it in different locations. If you are not creating a Python package, then you do not need to worry about what a pyproject.toml file is. 

If you have ever created a Python package before, then you should be familiar with a setup.py file. The pyproject.toml file is a similar configuration file that is used in Python packaging and it should be located in the same directory as the setup.py file. If you have never created a Python package before and you want to learn more, feel free to check out our tutorial on creating a Python package to learn more. 

What is a pyproject.toml file used for?

What is a pyproject.toml file used for? Python comes along with an internal set of tools that are used to build and distribute Python packages. This includes some modules you may have seen before such as setuptools and wheel. The pyproject.toml file gives you a way to specify which versions of the tools that are used to build your Python package. For example, if your package needs to be built using a specific version of setup tools, then you can specify that in your pyproject.toml file.

When was the pyproject.toml file introduced?

Are you wondering why you have never seen a pyproject.toml file before? That is because the pyproject.toml file was not always part of the Python packaging process. So when was the pyproject.toml file introduced to the Python ecosystem? The groundwork for the pyproject.toml file was laid out in PEP 517 which was created in 2015 and PEP 518 which was created in 2016. 

Why should you use a pyproject.toml file

Why should you use a pyproject.toml file when you are creating your Python packages? There are a few reasons that you should use a pyproject.toml file when creating a Python package. 

The main advantage of using a pyproject.toml file is that, as we said before, it makes it easy to specify which versions of Python’s internal build tools you want to use to build your package. Specifying the exact version of Python’s build tools that should be used to build your package guards against future bugs that might occur if your package is built with a version of the build tools you never tested when you were developing your package.

So what if you do not think your Python package is going to be rebuilt many times in the future? Does that mean that you do not need to include a pyproject.toml file along with your Python package? Not necessarily. Even if you do not think your project will be rebuilt many times in the future, you should still include a pyproject.toml file when you build your Python package because it is a standard file that developers expect to see when they look at the source code for a Python package. You should always keep up with the current coding standards when you are developing Python packages because it makes your code easier for other developers to read and understand your code. 

What does a pyproject.toml file look like?

What does a pyproject.toml file look like? Here is a basic example of what a pyproject.toml file should look like. This file simply states that setuptools and wheel are required to build the Python package and the version of setuptools that is used should be 42 or higher. You should use setuptools 42 or higher when using a pyproject.toml file because 42 is the first version of setuptools that was configured to read certain configurations from the pyproject.toml file.

[build-system]
requires = [
    "setuptools>=42",
    "wheel"
]
build-backend = "setuptools.build_meta"

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