Fixing glib 2.82.5 Upgrade Failures on macOS: Resolving Python Dependency Issues with Homebrew

Learn how to fix Python dependency errors when upgrading glib to 2.82.5 via Homebrew on macOS, especially when using conda-managed Python environments.
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Introduction

Upgrading glib to version 2.82.5 on macOS via Homebrew can sometimes fail due to Python dependency detection errors during the build process. This is especially common if your system uses a conda-managed Python environment or a non-standard Homebrew installation path.

The Problem

When running brew upgrade glib, the meson build system may fail with an error like:

[[See Video to Reveal this Text or Code Snippet]]

Even if the Python pkg-config files exist (e.g., python3.pc), the build script cannot find the Python headers and libraries.

Why This Happens

Meson tries to locate Python via pkg-config or system Python paths, which may not align with Homebrew's Python or your conda environment.

Environment variables like PYTHONPATH pointing to conda-managed binaries don’t help meson find Python headers.

Homebrew formula uses Meson to build gobject-introspection as a resource inside glib; it needs explicit include paths for Python headers.

The Solution

Step 1: Install a Compatible Python Version Via Homebrew

Even if you use conda, glib's build expects a Homebrew Python, e.g.:

[[See Video to Reveal this Text or Code Snippet]]

Replace 3.13 with the version matching your Homebrew Python if different.

Step 2: Modify the glib Formula to Explicitly Provide Python Include Paths

Locate the glib formula Ruby file (usually in Homebrew’s core tap) and edit it.

Insert these lines before the block that stages gobject-introspection:

[[See Video to Reveal this Text or Code Snippet]]

Note: Adjust the Python version and the Homebrew prefix path if you installed Homebrew in a custom location (e.g., /Applications/homebrew). Use full absolute paths if necessary.

Why This Works

PKG_CONFIG_PATH ensures pkg-config can locate Python .pc files.

CPATH tells the compiler where the Python headers are, enabling Meson to find Python during the build.

Step 3: Build or Upgrade glib Normally

With these environment variables set, running:

[[See Video to Reveal this Text or Code Snippet]]

should succeed without the Python dependency error.

Additional Notes

Resetting or clearing PYTHONPATH is not enough because Meson requires development headers, not just runtime libraries.

This workaround is necessary until upstream Homebrew formula or Meson scripts fully support conda or other Python environments transparently.

Summary

To fix Python dependency errors when upgrading glib via Homebrew:

Ensure Homebrew Python is installed and used for building.

Add explicit include paths for Python headers in the glib formula.

Adjust PKG_CONFIG_PATH and CPATH environment variables accordingly.

This approach helps Meson locate Python, enabling a smooth upgrade of glib to 2.82.5 on macOS.