on writing a while loop for rolling two dice

[Hope Rouselle]

"Peter J. Holzer" <hjp-python at hjp.at> writes:

> On 2021-09-02 11:28:21 -0300, Hope Rouselle wrote:
>> dn <PythonList at DancesWithMice.info> writes:
>> > On 29/08/2021 08.46, Hope Rouselle wrote:
>> >> Here's my solution:
>> >> 
>> >> --8<---------------cut here---------------start------------->8---
>> >> def how_many_times():
>> >>   x, y = 0, 1
>> >>   c = 0
>> >>   while x != y:
>> >>     c = c + 1
>> >>     x, y = roll()
>> >>   return c, (x, y)
>> >
>> >> 
>> >> Why am I unhappy?  I'm wish I could confine x, y to the while loop.
>> >> The introduction of ``x, y = 0, 1'' must feel like a trick to a
>> >> novice.  How would you write this?
> [...]
>> But perhaps we may agree that while rolling dice until a certain
>> success, we want to roll them while something happens or doesn't happen.
>> One of the two.  So while-True is a bit of a jump.  Therefore, in this
>> case, the easier and more natural option is to say while-x-not-equal-y.
>> 
>> But this approach seems to force me into initializing x, y with
>> different values.
>
> You can get around this by using NaN:
>
> def how_many_times():
>   c, x, y = 0, math.nan, math.nan
>   while x != y:
>     c = c + 1
>     x, y = roll()
>   return c, x, y
>
> Not sure if this is an improvement. Now you have to explain to your
> students why math.nan != math.nan.
>
> When I need a guaranteed unique value I often just use object():
>
> def how_many_times():
>   c, x, y = 0, object(), object()
>   while x != y:
>     c = c + 1
>     x, y = roll()
>   return c, x, y
>
> Of course now you are back to two different values, but they look the
> same. Which may be better or worse for your students. Plus x and y are
> now bound to objects of different types during their lifetime, which may
> be a bit dicey.

Lol.  I would argue that it's quite appropriate to the event (``of
rolling dice'' --- clarity-obsession). :D Pretty nice alternatives.
Thank you so much.