Build mpdecimal from source to workaround unreliable launchpad.net

[hugovk]

Canonical infra is unreliable right now:

• https://status.canonical.com/: "Canonical’s web infrastructure is under a sustained, cross-border attack and we are working to address it. We will provide more information in our official channels as soon as we are able to."
• https://www.theregister.com/2026/05/01/canonical_confirms_ubuntu_infrastructure_under/

This is causing the libmpdec-dev install to fail from ppa:ondrej/php and launchpad.net.

Instead, until things stabilise, we can temporarily build from source.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #32501975 | 📁 Comparing 5be4b5f against main (d96ffc1)

  🔍 Preview build  

24 files changed · ± 24 modified

± Modified

• contents.html
• download.html
• genindex-B.html
• genindex-C.html
• genindex-D.html
• genindex-E.html
• genindex-H.html
• genindex-I.html
• genindex-P.html
• genindex-R.html
• and 14 more...

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @hugovk, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 60b751c0181ec4f646666fb02bf4b44e3969e44c 3.14

[miss-islington-app]

Sorry, @hugovk, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 60b751c0181ec4f646666fb02bf4b44e3969e44c 3.13

[hugovk]

We don't actually need this for 3.14 (and likely 3.13) because it falls back to bundled libmpdec.

Both are still passing:

• https://github.com/python/cpython/actions/workflows/build.yml?query=branch%3A3.14
• https://github.com/python/cpython/actions/workflows/build.yml?query=branch%3A3.13