29.05.20 12:48, Mark Dickinson пише:
2. Call the object's `__float__` method. But this is fraught with peril, too: for a proper equivalent, you need to be careful to look up `__float__` on the type, not the object itself. And then a new version of Python changes `PyFloat_AsDouble` to also accept objects with `__index__`, and suddenly your version no longer matches what Python does. (This happened.)
There is yet one problem with calling the object's `__float__` method. It looks up `__float__` as object's attribute instead of type's attribute, so it is possible to override it for individual object.
So my modest proposal is: expose the conversion represented by `PyFloat_AsDouble` to Python somewhere: either on the `float` type itself, or somewhere in the standard library. My question for everyone on this list is: _if_ it were to be added, where should it go? (There's also the "what should it be called" question, of course.)
I prefer it to be an alternative float constructor. We can also add the corresponding constructor for complex, and add constructors which accept only str, bytes or bytes-like object (i.e. parse a text representation of the number). See also previous discussion about alternative constructors. [1]
[1] https://mail.python.org/archives/list/python-ideas@python.org/thread/5JKQMIC6EUVCD7IBWMRHY7DRTTNSBOWG/
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