possible bug in while loop test

[MRAB]

On 2017-09-02 18:53, Charles Hixson wrote:
> python3 --version
> Python 3.5.3
> 
> Running on Debian stretch
> 
> In this code s is a string parameter
> 
> while (j < k   and \
>            (s[j].isalnum())      or   \
>             (s[j] in seps and s[j+1].isalnum()) ):
>      j   =   j + 1
>      print ("i = {0}, j = {1}, k = {2}, len[s] = {3}".   \
>            format(i, j, k, len(s) ) )
> 
> Yields the result:
> 
> i = 25, j = 27, k = 31, len[s] = 32
> i = 25, j = 28, k = 31, len[s] = 32
> i = 25, j = 29, k = 31, len[s] = 32
> i = 25, j = 30, k = 31, len[s] = 32
> i = 25, j = 31, k = 31, len[s] = 32
> Traceback (most recent call last):
>     File "parse1.py", line 40, in <module>
>       print (parse1("The gostack distimms the doshes."))
>     File "parse1.py", line 21, in parse1
>       (s[j] in seps and s[j+1].isalnum()) ):
> IndexError: string index out of range
> 
> I hesitate to report this, because I've been wrong so often, but it
> looks to me like the last iteration should not have happened since j is
> not less than k.
> 
The last iteration happened because j < k when you tested the while 
loop's condition.

You then added 1 to j before printing out j and k. At this print, j >= k.