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Date: Fri, 19 Apr 2013 17:05:41 +1000
Subject: Re: The type/object distinction and possible synthesis of OOP and imperative programming languages
From: Chris Angelico <rosuav@gmail.com>
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On Fri, Apr 19, 2013 at 1:35 PM, rusi <rustompmody@gmail.com> wrote:
> If I have a loop:
>
>  while i < len(a) and a[i] != x:
>    i++
>
> I need to understand that at the end of the loop:
> i >= len(a) or a[i] == x
> and not
> i >= len(a) and a[i] == x
> nor
> i == len(a) or a[i] == x  # What if I forgot to initialize i?

Or your program has crashed out with an exception.

>>> i,a,x=-10,"test","q"
>>> while i < len(a) and a[i] != x:
	i+=1

Traceback (most recent call last):
  File "<pyshell#69>", line 1, in <module>
    while i < len(a) and a[i] != x:
IndexError: string index out of range

Or if that had been in C, it could have bombed with a segfault rather
than a nice tidy exception. Definitely initialize i.

But yeah, the basis of algebra is helpful, even critical, to
understanding most expression evaluators.

ChrisA