recursion depth problem

[Steven Bethard]

Alex Martelli wrote:
> Steven Bethard <steven.bethard at gmail.com> wrote:
>    ...
>>>>>>> import sys
>>>>>>> def ch4(item, n=0):
>>>>>>>    if n < len(item):
>>>>>>>            if item[n] == '0':
>>>>>>>                    item[n] = '1'
>>>>>>>                    print ''.join(item)
>>>>>>>                    ch4(item)
>>>>>>>            elif item[n] == '1':
>>>>>>>                    item[n] = '0'
>>>>>>>                    ch4(item, n+1)
>>>>>>> ch4(list(sys.argv[1]))
>    ...
>>> for interest sake:  is my method unredeemable?
>> Let's just say that I don't currently see an obvious way of redeeming
>> it. ;-)
> 
> Change the outer if into a while, and the recursive calls into proper
> assignments to n.  They're both tail-recursive calls, so this won't
> change the semantics, as it happens.

Thanks!

     >>> def f(chars):
     ...     n = 0
     ...     while n < len(chars):
     ...         if chars[n] == '0':
     ...             chars[n] = '1'
     ...             n = 0
     ...             print ''.join(chars)
     ...         elif chars[n] == '1':
     ...             chars[n] = '0'
     ...             n += 1
     ...
     >>> f(list('00000000'))
     10000000
     01000000
     11000000
     ...
     10111111
     01111111
     11111111

Looks good.

STeVe