In the instructions below, replace pip as needed with a pip invocation matching your target Python environment (eg, pip3, /usr/local/bin/python3.11 -m pip).

Pre-seed wheel cache (recommended)

This solution pre-seeds pip's wheel cache with a locally-built PyYAML wheel, accessible to any subsequent installation using the same pip cache.

# create a constraint file that limits the Cython version to one that should work
echo 'Cython < 3.0' > /tmp/constraint.txt

# seed pip's local wheel cache with a PyYAML wheel
PIP_CONSTRAINT=/tmp/constraint.txt pip wheel PyYAML==5.4.1

# install PyYAML itself, or any other package(s) that ask for the PyYAML version you just built
pip install 'PyYAML==5.4.1'

Inline constraint (simpler, more likely to break)

This solution globally constrains the Cython version for all packages being installed by this pip invocation (including nested/child package installs), which could break other packages installed at the same time.

# create a constraint file that limits the Cython version to one that should work
echo 'Cython < 3.0' > /tmp/constraint.txt

# install PyYAML itself (or other packages that need it); any package requiring Cython will be constrained to `Cython < 3.0`
PIP_CONSTRAINT=/tmp/constraint.txt pip install 'PyYAML==5.4.1'

Background

With the release of Cython 3, all older versions of PyYAML can no longer be installed from unmodified source or sdist (ie, where a wheel is unavailable for the platform and/or Python), since the Cython version was not capped to a working version for all older PyYAML releases. For various reasons, it is untenable to release new sdists/wheels for these old PyYAML versions with the new required Cython<3.0 build dependency constraint.

pip has mostly-undocumented support for "inherited" constraints at install-time by setting the PIP_CONSTRAINT environment variable (which is inherited by child build processes, unlike the CLI --constraint arg).

Sample error output from pip install

If you're seeing an error similar to this when installing a version of PyYAML older than 6.0.1, the preceding solutions may help.

...
  error: subprocess-exited-with-error
  
  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [48 lines of output]
      running egg_info
      writing lib/PyYAML.egg-info/PKG-INFO
      writing dependency_links to lib/PyYAML.egg-info/dependency_links.txt
      writing top-level names to lib/PyYAML.egg-info/top_level.txt
      Traceback (most recent call last):

...

          raise AttributeError(attr)
      AttributeError: cython_sources
      [end of output]