[Python-ideas] BUG in standard while statement

[David Blaschke]

while repeat(2): creates a new repeat instance each time through the
loop and initializes the variable as 2 each time through the loop i.e.
repeat(2) returns a new, different instance each time.

On 9/9/15, Stephan Sahm <Stephan.Sahm at gmx.de> wrote:
> Dear all
>
> I found a BUG in the standard while statement, which appears both in python
> 2.7 and python 3.4 on my system.
>
> It usually won't appear because I only stumbled upon it after trying to
> implement a nice repeat structure. Look:
> ​```​
> class repeat(object):
>     def __init__(self, n):
>         self.n = n
>
>     def __bool__(self):
>         self.n -= 1
>         return self.n >= 0
>
>     __nonzero__=__bool__
>
> a = repeat(2)
> ```
> the meaning of the above is that bool(a) returns True 2-times, and after
> that always False.
>
> Now executing
> ```
> while a:
>     print('foo')
> ```
> will in fact print 'foo' two times. HOWEVER ;-) ....
> ```
> while repeat(2):
>     print('foo')
> ```
> will go on and go on, printing 'foo' until I kill it.
>
> Please comment, explain or recommend this further if you also think that
> both while statements should behave identically.
>
> hoping for responses,
> best,
> Stephan
>


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