Adding a float to an integer using a method (not an operator) [duplicate]

问题

This question already has answers here:

Difference between a+b and a.__add__(b) (1 answer)

Python: __add__ and +, different behavior with float and integer (1 answer)

Closed 16 days ago.

I was expecting __add__ to work, but that's obviously not the case (in Python 3.8.0 at least):

>>> 10 .__add__(5.5)  
NotImplemented
>>> 10 .__radd__(5.5) 
NotImplemented

The other way around works:

>>> 5.5 .__add__(10)  
15.5
>>> 5.5 .__radd__(10)  
15.5

Why doesn't the first code work? Is there a good reason behind it?

If those methods don't work, then what method is used by "syntactic sugar" operations such as 10 + 5.5 or 10 - 5.5?

来源：https://stackoverflow.com/questions/59644166/adding-a-float-to-an-integer-using-a-method-not-an-operator