Limiting versions of python used while building a formula

[rgoldberg]

Output of brew config

n/a

Output of brew doctor

n/a

Description of issue

Various formulae have build dependencies on multiple versions of python (e.g., , cryptography depends on [email protected], [email protected], and [email protected]).

When installing/upgrading, can I limit the build / build dependencies to just one of them?

If so, must I manually specify what python versions to use/skip? Or can I just say: only build for the python versions that are currently installed?

All of my installed python formulae have [email protected] as their runtime dependency.

At the least, I'd prefer to be able to ignore 3.11 (i.e. not install 3.11 for build, and not output 3.11 versions of the formulae), because I presumably will never use 3.11 again.

[SMillerDev]

No, this is not possible. Builds will only every build what is defined in the formula, there is no method to modify this.

[rgoldberg]

Thanks for the info. Do you think it would be difficult to add in a flag to brew install that makes it ignore certain dependencies & to add support in formulae to ignore a block if a dependency was ignored? Presumably, this info would have to be remembered for subsequent brew upgrades to follow suit.

[p-linnane]

You can create your own tap and do whatever you want, but we wouldn't support something like this.

[cho-m]

For cryptography specifically, one thing that may be possible is updating formula to build a single copy of cryptography and symlinking it since it builds in limited-API / ABI-stable mode.

However, this is only possible for Python packages that support this. For example, cryptography's dependency cffi doesn't (you can see that official wheels are Python minor version specific - https://pypi.org/project/cffi/#files). So, would still need multiple Pythons if building cryptography on a fresh system in order to build cffi.

Also, Python 3.11 usage should be removed as part of current Python 3.13 migration. Just need 0 dependents usage. Same thing as last migration - Homebrew/homebrew-core#156970

[rgoldberg]

@cho-m Will brew ever require that all formulae that are written in Python use something like pipx, so there won't be inter-formula dependencies like awscli on cryptography (which would also remove my need for cffi)?

[cho-m]

No, some formulae will remain as dependencies for documented reasons¹. We use cryptography formula to help prevent rust propagation and also to get latest security updates.

Footnotes

1. https://docs.brew.sh/Python-for-Formula-Authors#examples-of-allowed-libraries-in-homebrew-core ↩

[rgoldberg]

@cho-m I don't have experience with directly using Rust.

Brew installs various different languages & build systems to build formulae, so just wondering: why is Rust of singular concern? Are there many incompatible versions of Rust, so, compared to 3 installs of Python for builds, there'd be like 30 installs of Rust for builds? Or is it something else?

Thanks.

[quackerex]

Maybe you can use --ignore-dependencies