[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I think an alternative constructor is the best option. Some time ago I proposed 
to add more alternative constructors: 
https://mail.python.org/archives/list/python-id...@python.org/thread/5JKQMIC6EUVCD7IBWMRHY7DRTTNSBOWG/

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[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Mark Dickinson]

Mark Dickinson  added the comment:

On naming, maybe float.from_number or float.from_numeric?

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[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Mark Dickinson]

Mark Dickinson  added the comment:

> `operator` seems a slightly odd place for this.

Yes, it's not ideal. It's by analogy with operator.index, which provides the 
equivalent duck-typing for integers, and calls __index__.  Similarly, 
operator.as_float is primarily there to call __float__, except that now that 
PyFloat_AsDouble also makes use of __index__, it'll call that, too.

My other thought was putting this in math, since it's what the math module is 
already doing implicitly to most inputs.

An alternative float constructor could work. Though we then run into the messy 
question of what it should do for float subclasses ...

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[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Zachary Ware]

Zachary Ware  added the comment:

`operator` seems a slightly odd place for this.  My naive expectation would be 
that `float(floatlike_obj)` should do what you want, but it seems that's not 
the case (too permissive of input types?).  So then, what about an alternate 
constructor on the float object, `float.from_floatlike(obj)`?  This could be 
implemented as effectively:

class float:
@classmethod
def from_floatlike(cls, obj):
return cls(PyFloat_FromDouble(PyFloat_AsDouble(obj)))

which would work to get an instance of any float subclass after a round-trip 
through a double.  I have no idea whether that's actually useful, though :)

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nosy: +zach.ware

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[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Mark Dickinson]

Mark Dickinson  added the comment:

Proof of concept in GH-20481

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[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Mark Dickinson]

Change by Mark Dickinson :


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keywords: +patch
pull_requests: +19730
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/20481

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[issue40801] Expose PyFloat_ToDouble at Python level: operator.as_float?

[Mark Dickinson]

Change by Mark Dickinson :


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title: Expose PyFloat_ToDouble at Python level: operator.to_float? -> Expose 
PyFloat_ToDouble at Python level: operator.as_float?

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