[Python-Dev] Rounding float to int directly (Re: struct module and coercing floats to integers)

James Y Knight foom at fuhm.net
Fri Aug 4 04:02:34 CEST 2006

On Aug 3, 2006, at 2:34 AM, Greg Ewing wrote:

> Raymond Hettinger wrote:
>> -1 on an extra built-in just to save the time for function call
> The time isn't the main issue. The main issue
> is that almost all the use cases for round()
> involve doing an int() on it afterwards. At
> least nobody has put forward an argument to
> the contrary yet.

And I bet the main reason why round() in python returns a float is  
because it does in C.

And it does in C because C doesn't have arbitrary size integers, so  
if round returned integers, round(1e+308) couldn't work. In python,  
however, that's no problem, since python does have arbitrarily big  

There's also round(float("inf")), of course, which wouldn't be  
defined if the result was an integer, but I don't think rounding  
infinity is much of a use case.

And I do think the extension of round to allow the specification of  
number of decimal places was a mistake. If you want that, you  
probably really mean to do something like round(x * 10**y) instead.


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