[Tutor] A better way for greatest common divisor

[David Hutto]

On Sat, Jul 31, 2010 at 12:43 AM, David Hutto <smokefloat at gmail.com> wrote:
> 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
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>>
>
> 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.
>

however, had it been a math exercise, I would have sucked in boiling
it down, initially.