What is Python's coerce() used for?

Question

What are common uses for Python's built-in coerce function? I can see applying it if I do not know the type of a numeric value as per the documentation, but do other common usages exist? I would guess that coerce() is also called when performing arithmetic computations, e.g. x = 1.0 +2. It's a built-in function, so presumably it has some potential common usage?

Answer 1

Its a left over from early python, it basically makes a tuple of numbers to be the same underlying number type e.g.

>>> type(10) <type 'int'> >>> type(10.0101010) <type 'float'> >>> nums = coerce(10, 10.001010) >>> type(nums[0]) <type 'float'> >>> type(nums[1]) <type 'float'> 

It is also to allow objects to act like numbers with old classes
(a bad example of its usage here would be ...)

>>> class bad: ...     """ Dont do this, even if coerce was a good idea this simply ...         makes itself int ignoring type of other ! """ ...     def __init__(self, s): ...             self.s = s ...     def __coerce__(self, other): ...             return (other, int(self.s)) ...  >>> coerce(10, bad("102")) (102, 10)