I have a private package that won’t be distributed

If your package isn’t shared publicly, i.e. outside your company, organization or household, it usually isn’t strictly necessary to include a formal license, so you wouldn’t necessarily have to do anything extra here.

However, it is still a good idea to include LicenseRef-Proprietary as a license expression in your package configuration, and/or a copyright statement and any legal notices in a LICENSE.txt file in the root of your project directory, which will be automatically included by packaging tools.

I just want to share my own work without legal restrictions

While you aren’t required to include a license, if you don’t, no one has any permission to download, use or improve your work, so that’s probably the opposite of what you actually want. The MIT license is a great choice instead, as it’s simple, widely used and allows anyone to do whatever they want with your work (other than sue you, which you probably also don’t want).

To apply it, just paste the text into a file named LICENSE.txt at the root of your repo, and add the year and your name to the copyright line. Then, just add license = "MIT" under [project] in your pyproject.toml if your packaging tool supports it, or in its config file/section. You’re done!

I want to distribute my project under a specific license

To use a particular license, simply paste its text into a LICENSE.txt file at the root of your repo, if you don’t have it in a file starting with LICENSE or COPYING already, and add license = "LICENSE-ID" under [project] in your pyproject.toml if your packaging tool supports it, or else in its config file. You can find the LICENSE-ID and copyable license text on sites like ChooseALicense or SPDX.

Many popular code hosts, project templates and packaging tools can add the license file for you, and may support the expression as well in the future.

I maintain an existing package that’s already licensed

If you already have license files and metadata in your project, you should only need to make a couple of tweaks to take advantage of the new functionality.

In your project config file, enter your license expression under license ([project] table in pyproject.toml), or the equivalent for your packaging tool, and make sure to remove any legacy license table subkeys or License :: classifiers. Your existing license value may already be valid as one (e.g. MIT, Apache-2.0 OR BSD-2-Clause, etc); otherwise, check the SPDX license list for the identifier that matches the license used in your project.

Make sure to list your license files under license-files.paths or license-files.globs under [project] in pyproject.toml or else in your tool’s configuration file.

See the Basic example for a simple but complete real-world demo of how this works in practiced. Packaging tools may support automatically converting legacy licensing metadata; check your tool’s documentation for more information.

My package includes other code under different licenses

If your project includes code from others covered by different licenses, such as vendored dependencies or files copied from other open source software, you can construct a license expression to describe the licenses involved and the relationship between them.

In short, License-1 AND License-2 mean that both licenses apply to your project, or parts of it (for example, you included a file under another license), and License-1 OR License-2 means that either of the licenses can be used, at the user’s option (for example, you want to allow users a choice of multiple licenses). You can use parenthesis (()) for grouping to form expressions that cover even the most complex situations.

In your project config file, enter your license expression under license ([project] table of pyproject.toml), or the equivalent for your packaging tool, and make sure to remove any legacy license table subkeys or License :: classifiers.

Also, make sure you add the full license text of all the licenses as files somewhere in your project repository. List the relative path or glob patterns to each of them under license-files.paths or license-files.globs under [project] in pyproject.toml (if your tool supports it), or else in your tool’s configuration file.

As an example, if your project was licensed MIT but incorporated a vendored dependency (say, packaging) that was licensed under either Apache 2.0 or the 2-clause BSD, your license expression would be MIT AND (Apache-2.0 OR BSD-2-Clause). You might have a LICENSE.txt in your repo root, and a LICENSE-APACHE.txt and LICENSE-BSD.txt in the _vendor subdirectory, so to include all of them, you’d specify ["LICENSE.txt", "_vendor/packaging/LICENSE*"] as glob patterns, or ["LICENSE.txt", "_vendor/LICENSE-APACHE.txt", "_vendor/LICENSE-BSD.txt"] as literal file paths.

See a fully worked out Advanced example for an end-to-end application of this to a real-world complex project, with many technical details, and consult a tutorial for more help and examples using SPDX identifiers and expressions.