The degree character (°) causes a decode error

[Paebbels]

Describe the bug

When documenting code with embedded ReST in Python classes, the degree character ° like in 90° causes a decode error:

C:\Git\GitHub\pyTooling\pyTooling\doc\pyTooling\pyTooling.Cartesian2D.Shapes.rst:24: WARNING: undecodable source characters, replacing with "?": b' A rectangle is a trapezium, where opposite edges a parallel to each other and all inner angels are 90>>>\xb0<<<.\r'

class Rectangle(Trapezium[Coordinate]):
	"""
	A rectangle is a trapezium, where opposite edges a parallel to each other and all inner angels are 90°.
	"""

Source: https://github.com/pyTooling/pyTooling/blob/main/pyTooling/Cartesian2D/Shapes.py#L112

Shouldn't standard Unicode characters encoded in UTF-8 just work out of the box?

How to Reproduce

class Rectangle:
  """
  A rectangle is a trapezium, where opposite edges a parallel to each other and all inner angels are 90°.
  """

If needed, I could strip down the overall documentation to a standalone problem.

Environment Information

Sphinx version: v9.0.4

Sphinx extensions

extensions = [
  "sphinx.ext.autodoc",
  "autoapi.sphinx"
]

Additional context

As a workaround, ... 90\ |deg|\ . can be used. Therefore, isonum.txt must be included.

.. # Load pre-defined aliases and graphical characters like © from docutils
   # <file> is used to denote the special path
   # <Python>\Lib\site-packages\docutils\parsers\rst\include
.. include:: <isonum.txt>

[Paebbels]

As °/|deg| is a standalone character, why isn't it defined in isonum.txt with :trim:?
Maybe because if trimming is on, it will eat up all spaces, thus it can't be used with space at all. (?)

When I redefine it as

.. # Loaded in the prolog file
.. include:: <isonum.txt>

.. # Local definition
.. |deg| unicode:: U+00B0
   :trim:

I get this error:

<rst_prolog>:7: ERROR: Duplicate substitution definition name: "deg". [docutils]

It would be nice if users could redefine replacements, right?
Of cause it's also good to indicate a possible error my warning of a redefinition.

[jfbu]

If possible, could you provide some minimal example. I could not reproduce the issue with a minimal project using sphinx.ext.autodoc and .. automodule:: with Docutils 0.22.3.

[Paebbels]

OK, I'll create one.

But in general, this unicode character should work out of the box, right?

[AA-Turner]

Yes, UTF-8 encoded sources should work. Can you upload the exact files used in a zip archive so I can check for encoding errors?

A