The C-API docs says: "Return the real/imag part of op as a C double." But the real code looks like:

PyComplex_RealAsDouble(PyObject*op){if (PyComplex_Check(op)) {return ((PyComplexObject*)op)->cval.real;    }else {returnPyFloat_AsDouble(op);    }}

So, we assume instead that theop is a float-like class (a subtype of or something with a__float__ dunder method). Instead, we should look on the__complex__ method in theelse branch. This is an issue like#44670, I think.

Minor issue: these functions aren't tested, only indirectly withformat() (that will not trigger all possible cases).

Edit:
The currentPyComplex_ImagAsDouble() silently returns0.0 for all non-PyComplexObject objects (or subtypes of). I think it's a bug and we should return-1.0 instead and set the error indicator.

Linked PRs

• gh-109598: make PyComplex_RealAsDouble/ImagAsDouble use __complex__ #109647