pip install scitools-iris error in subprocess (getting requirements to build wheel)

Question

When I was trying to install scitools-iris, I received an error saying "Getting requirements to build wheel did not run successfully." I followed the installation directions in https://scitools-iris.readthedocs.io/en/latest/installing.html#installing-from-source-without-conda-on-debian-based-linux-distros-developers.

Collecting cf-units~=3.0.1
  Using cached cf-units-3.0.1.post0.tar.gz (162 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error
  
  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [51 lines of output]
      Compiling cf_units/_udunits2.pyx because it depends on /tmp/pip-build-env-gy2i_ubf/overlay/local/lib/python3.10/dist-packages/Cython/Includes/libc/string.pxd.
      [1/1] Cythonizing cf_units/_udunits2.pyx
      running egg_info
      Traceback (most recent call last):
        File "/usr/lib/python3/dist-packages/pip/_vendor/pep517/in_process/_in_process.py", line 363, in <module>
          main()
        File "/usr/lib/python3/dist-packages/pip/_vendor/pep517/in_process/_in_process.py", line 345, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
        File "/usr/lib/python3/dist-packages/pip/_vendor/pep517/in_process/_in_process.py", line 130, in get_requires_for_build_wheel
          return hook(config_settings)
        File "/usr/lib/python3/dist-packages/setuptools/build_meta.py", line 162, in get_requires_for_build_wheel
          return self._get_build_requires(
        File "/usr/lib/python3/dist-packages/setuptools/build_meta.py", line 143, in _get_build_requires
          self.run_setup()
        File "/usr/lib/python3/dist-packages/setuptools/build_meta.py", line 158, in run_setup
          exec(compile(code, __file__, 'exec'), locals())
        File "setup.py", line 155, in <module>
          setup(**kwargs)
        File "/usr/lib/python3/dist-packages/setuptools/__init__.py", line 153, in setup
          return distutils.core.setup(**attrs)
        File "/usr/lib/python3/dist-packages/setuptools/_distutils/core.py", line 148, in setup
          return run_commands(dist)
        File "/usr/lib/python3/dist-packages/setuptools/_distutils/core.py", line 163, in run_commands
          dist.run_commands()
        File "/usr/lib/python3/dist-packages/setuptools/_distutils/dist.py", line 967, in run_commands
          self.run_command(cmd)
        File "/usr/lib/python3/dist-packages/setuptools/_distutils/dist.py", line 986, in run_command
          cmd_obj.run()
        File "/usr/lib/python3/dist-packages/setuptools/command/egg_info.py", line 299, in run
          self.find_sources()
        File "/usr/lib/python3/dist-packages/setuptools/command/egg_info.py", line 306, in find_sources
          mm.run()
        File "/usr/lib/python3/dist-packages/setuptools/command/egg_info.py", line 541, in run
          self.add_defaults()
        File "/usr/lib/python3/dist-packages/setuptools/command/egg_info.py", line 578, in add_defaults
          sdist.add_defaults(self)
        File "/usr/lib/python3/dist-packages/setuptools/_distutils/command/sdist.py", line 226, in add_defaults
          self._add_defaults_python()
        File "/usr/lib/python3/dist-packages/setuptools/command/sdist.py", line 113, in _add_defaults_python
          self._add_data_files(self._safe_data_files(build_py))
        File "/usr/lib/python3/dist-packages/setuptools/command/egg_info.py", line 622, in _safe_data_files
          return build_py.get_data_files_without_manifest()
        File "/usr/lib/python3/dist-packages/setuptools/command/build_py.py", line 78, in get_data_files_without_manifest
          return list(map(self._get_pkg_data_files, self.packages or ()))
        File "/usr/lib/python3/dist-packages/setuptools/command/build_py.py", line 90, in _get_pkg_data_files
          for file in self.find_data_files(package, src_dir)
        File "/usr/lib/python3/dist-packages/setuptools/command/build_py.py", line 96, in find_data_files
          patterns = self._get_platform_patterns(
        File "/usr/lib/python3/dist-packages/setuptools/command/build_py.py", line 214, in _get_platform_patterns
          spec.get('', []),
      AttributeError: 'NoneType' object has no attribute 'get'
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error

× Getting requirements to build wheel did not run successfully.
│ exit code: 1
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.