Decimal as implemented in _pydecimal supports the '#' alternate form in format strings, though this does not appear to be documented: as with floats, it causes a decimal point to be included regardless of value.  Decimal as implemented in cdecimal, as it uses libmpdec, does not.

This is a rather minor discrepancy; I hadn't actually intended to have # in my format string at all, but it had ended up there and was causing errors for half of the users of my library.  # also could be useful for decimals, as it can be for floats.

Like #45739, it's unclear to me whether this is a discrepancy that should be corrected by implementing # for cdecimal, removing # support for _pydecimal, or just documenting the inconsistency.