for / while else doesn't make sense

[Ben Bacarisse]

Chris Angelico <rosuav at gmail.com> writes:

> On Tue, May 24, 2016 at 2:51 AM, Ben Bacarisse <ben.usenet at bsb.me.uk> wrote:
>> Chris Angelico <rosuav at gmail.com> writes:
>>
>>> On Tue, May 24, 2016 at 12:29 AM, Ben Bacarisse <ben.usenet at bsb.me.uk> wrote:
>>>> Right, but this is to miss the point.  Let's say that 4000 years have
>>>> defined 1/3 to be one third, but Python 3 (as do many programming
>>>> languages) defines 1/3 to be something very very very very close to one
>>>> third, and *that* idea is very very very very new!
>>>
>>> Have you ever written one third as 0.33333333 ?
>>
>> Not that I recall, but, obviously, I can't be sure.  I can't even tell
>> without counting how many 3s there are there.  Why do you ask?
>>
>>> Because that's also
>>> something very very close to one third.
>>
>> Yes it is, but I don't get what point you are making.
>
> You asserted that representing one third as something almost, but not
> exactly, one third was a new idea.

Ah, I didn't mean to assert that at all.  I meant to say that the new
thing is that the approximation is tucked away in a representation
largely hidden from the person doing the arithmetic.  Its floats in
programming languages that are new, not approximations.

> It is not. Ever since ancient
> times, approximations have been used. Python is no different from
> anything else; the only reason it _looks_ different is that it's an
> approximation in binary, converted to decimal for display.

It's often hard for people to see that actual value[1] in a program, but
not when they do arithmetic by hand.  This is what confused me about
your question.  Were I to approximate 1/3 with 0.333 (on paper) there
should be no surprises down the line.  I know that 3 times it won't be
1, but 0.999.  Confusion creeps in when the approximation is not
explicit in the eye of the beginner.  Obviously, to you and me, 1/3 is
clearly an approximation in Python -- we know that / explicitly makes
floats -- but not everyone knows the full consequences of that right
away.  I doubt anyone, beginner or not, would be surprised that
0.33333333 is not actually one third (though they *might* be surprised
if it's not 33333333/100000000).

[1] Not being a Python expert I don't know how you show that actual
value of a float.  What is the Pythonic way to do that?

-- 
Ben.