[Python-ideas] BUG in standard while statement

Stephan Sahm Stephan.Sahm at gmx.de
Wed Sep 9 19:10:18 CEST 2015

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


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:
will in fact print 'foo' two times. HOWEVER ;-) ....
while repeat(2):
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,
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