[Python-Dev] "result type only depends on operand types"...?

[Guido van Rossum]

> Back on March 10 in the thread on PEP 285 Guido wrote:
> 
> """
> This is a very general rule that I like a lot: that the type of a
> result should only depend on the type of the arguments, not on their
> values.  I expect that this rule will make reasoning about programs
> (as in PsyCo or PyChecker) easier to do.
> 
> I recently caved in and allowed an exception: 2**2 returns an int, but
> 2**-2 returns a float.  This was a case of "practicality beats
> purity".  I don't see True-1 in the same league though.
> """
> 
> And yet...:
> 
> >>> type(2**10)
> <type 'int'>
> >>> type(2**100)
> <type 'long'>
> 
> ...doesn't this apply to many operators on ints in 2.2?  Yet _another_
> (set of) exception(s) with practicality beating purity?  Perhaps, but if a 
> "very general rule" has so many exceptions in frequent and fundamental
> cases, is it a rule at all...?

Oh, go away.  That's part of PEP 237.

--Guido van Rossum (home page: http://www.python.org/~guido/)