[Tutor] Integer division (Was: Re: Format strings for variables - how?)

Kalle Svensson kalle@gnupung.net
Thu, 8 Feb 2001 09:11:29 +0100

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Sez David Porter:
> * Viktor Lakics <lakicsv@usa.net>:
> > a=3D1
> > b=3D3
> > print "%0.2f" %(a/b)
> >=20
> > The above code gives me 0.00 as a result, while I wanted to get
> > 0.33...
> The reason is that the numbers you are dividing are not floats. Because of
> that, you are doing integer division.
> >>> a =3D 1.0
> >>> b =3D 3
> print "%0.2f" %(a/b)
> gives 0.33. You must add a decimal point to one (or more) of the numbers.

Now, you might (should, I think) wonder:  Why?
Basically, I think there are two reasons python has integer division.

 1) C has truncating integer division.  Python is implemented in C.  Some of
the initial target users for Python were C programmers.

 2) There is no way to handle division of two integers that everybody likes.
Some want truncating integer division (chopping off the remainder), some wa=
conversion to float (which loses exact representation), some want rational
math (resource intensive), some want the Spanish Inquisition...

 3) It would break a lot of existing code if it was changed tomorrow.
Three reasons.

The way it works today is perhaps not the most obvious for a newcomer to
programming or one with experience in languages using different solutions,
but when you get used to it, it's at least as good as any of the
alternatives, IMHO.

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