Also, pyright (though not mypy) notes that since the keys of the FontMetricsHeader are not required, they may cause an exception later in the property getters. Do we want to validate that earlier in the constructor, or mark those are required because we only intend to load known-good files?

cc @jkseppan as you were going to do similar for _type1hint.py.

We should add a note to the dev docs that we are doing in-line type hints for private modules.

Also, pyright (though not mypy) notes that since the keys of the FontMetricsHeader are not required, they may cause an exception later in the property getters. Do we want to validate that earlier in the constructor, or mark those are required because we only intend to load known-good files?

Another option is to do something like

    def get_fontname(self) -> str:
        """Return the font name, e.g., 'Times-Roman'."""
        if 'FontName' not in self._header:
            raise LookupError(
                'Font name not found in AFM header. '
                'This may be due to an incomplete or malformed AFM file.'
            )
        return self._header['FontName']

for all of the accesses. The if statement lets pyright narrow the type.

We should add a note to the dev docs that we are doing in-line type hints for private modules.

Should we discuss the overall direction regarding type hints? There was some discussion on Gitter but since there clearly are different opinions, I don't think we should decide this too hastily.