division

[Ben Finney]

On Mon, 23 Jun 2003 01:44:54 +0100, kpop wrote:
> Hi, i am writing a maths program where i get input from the user and
> store it in a string. i then use the eval fucntion to return the right
> answer.

I wonder what sort of checking you're performing on the input, to
prevent users typing anything they like and having Python happily eval()
it.

> The problem is division, I would like it that only exact division was
> aloud, I mean no remainders.

Read about math.ceil() and math.floor():

    <http://www.python.org/doc/current/lib/module-math.html#l2h-905>
    <http://www.python.org/doc/current/lib/module-math.html#l2h-910>

> In python "22 / 5" returs an int of 5

Because both arguments to the division were specified as integers.  If
you make either argument a floating-point number, the result will also
be floating-point.

>>> 22 / 5
4
>>> 22.0 / 5
4.4000000000000004
>>> 22 / 5.0
4.4000000000000004
>>> import math
>>> math.floor( 22 / 5.0 )
4.0
>>> 

> i would like if that was illegal because 5 doesnt go into 22 , 4 times
> exactly, and have the eval function raise an execption which i could
> handle.

You want different behaviour to the existing arithmetic operators, which
try to return a meaningful result if possible, rather than raising an
exception.

> any advice?

I suppose you could create new numeric classes to raise exceptions when
they received input you don't like, but it seems like a lot of effort.
Better would be to validate the input better when it is received, so
that you didn't pass undesired inputs to the arithmetic.

Why not simply math.floor() the result, to force it to an integer?

-- 
 \        "Know what I hate most?  Rhetorical questions."  -- Henry N. |
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