Hypermodern Python Tooling by Claudio Jolowicz

Author:Claudio Jolowicz [Claudio Jolowicz]
Language: eng
Format: epub
ISBN: 9781098139582
Publisher: O'Reilly Media, Inc.
Published: 2024-04-25T00:00:00+00:00

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The Required Python Version

Use the project.requires-python field to specify the versions of Python that your project supports.6

[project] requires-python = ">=3.7"

Most commonly, people specify the minimum Python version as a lower bound, using a string with the format >=3.x. The syntax of this field is more general and follows the same rules as version specifiers for project dependencies (see Chapter 4).

Tools like Nox and tox make it easy to run checks across multiple Python versions, helping you ensure that the field reflects reality. As a baseline, I recommend requiring the oldest Python version that still receives security updates. You can find the end-of-life dates for all current and past Python versions on the Python Developer Guide.

There are three main reasons to be more restrictive about the Python version. First, your code may depend on newer language features—​for example, structural pattern matching was introduced in Python 3.10. Second, your code may depend on newer features in the standard library—​look out for the “Changed in version 3.x” notes in the official documentation. Third, it could depend on third-party packages with more restrictive Python requirements.

Some packages declare upper bounds on the Python version, such as >=3.7,<4. This practice is discouraged, but depending on such a package may force you to declare the same upper bound for your own package. Dependency solvers can’t downgrade the Python version in an environment; they will either fail or, worse, downgrade the package to an old version with a looser Python constraint. A future Python 4 is unlikely to introduce the kind of breaking changes that people associate with the transition from Python 2 to 3.

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