[Tutor] A better way for greatest common divisor

[David Hutto]

On Sat, Jul 31, 2010 at 12:37 AM, David Hutto <smokefloat at gmail.com> wrote:
> On Fri, Jul 30, 2010 at 11:51 PM, Steven D'Aprano <steve at pearwood.info> wrote:
>> On Sat, 31 Jul 2010 01:03:27 pm David Hutto wrote:
>>
>>> This fixes the floating point 'bug' when numerator is greater than
>>> denominator: http://python.pastebin.com/bJ5UzsBE
>>
>> I don't mean to be disparaging ... ah hell, who am I fooling? Yes I do.
>> What is that mess? *wink*
> It works except under [3], and that's fixable. And even, I know it's a
> good gradumacated the eighth grade, newbie attempt.*winks* back.
>>
>> I can see at least four problems with that:
>>
>> 1. You have a function called "gcd" that doesn't calculate the gcd, but
>> does something else as well. That makes it a misleading name.
>
> I still have the habit of wanting to use the functions like I would an
> instance of the functions.
>
>>
>> 2. The principles of code reuse and encapsulation suggest that each
>> function should (as much as possible) do one thing, and do it well. You
>> have a function that tries to do two or three things. You should have a
>> single function to calculate the gcd, and a second function to use the
>> gcd for reducing a fraction as needed, and potentially a third function
>> to report the results to the user.
>
> Then maybe I should have done a larger class of functions instead then?
>
>
>>
>> 3. Your function has a serious bug. To see it, call gcd(5, 5) and see
>> what it doesn't do.
>
> I'll get to it, but it seems like I had that in the original, not the
> revised, maybe not, but did all other test cases for it, other than
> that
>
>
>
>>
>> 4. Code duplication. Your function repeats fairly major chunks of code.
>> Copy-and-paste programming is one of the Deadly Sins for programmers.
>> The way to get rid of that is by encapsulating code in functions (see
>> point 1 above).
>
> I thought about putting certain print statements in a function, as
> well as seperating the gcd into a from fractions import *, with a
> different parameter for each if the returning if placed it into the
> called function, but it seemed a little *overkill*, when it worked
> well within the single function, with a few parameters placed in
> through an instance with input.
>
>>
>>
>>
>> --
>> Steven D'Aprano
>> _______________________________________________
>> Tutor maillist  -  Tutor at python.org
>> To unsubscribe or change subscription options:
>> http://mail.python.org/mailman/listinfo/tutor
>>
>

But, just to say, it started out as just trying to calculate the GCD
with your current python skills(not import fractions, and
print(gcd(3,9))for a practice exercise, and the rest is just the
input, and stated output.