[Tutor] for vs while

[bob gailer]

James wrote:
> All,
>
> I have a dumb question...hopefully someone can shed some light on the  
> difference between for and while in the situation below.
>
> I'm trying to iterate through a list I've created.  The list consists  
> of a command, followed by a 'logging' message (a message printed to a  
> console or log file after the command is run).
>
> Here's a small snippet of code:
>
> 	# a list which includes (1) a command, and (2) something to be  
> dumped into a log file after the command runs
> 	stuff = [ ["cat /etc/password"] , ["viewed /etc/password"] ]
>
> 	#works
> 	i = 0 ; j = 1
> 	while i < len( stuff ):
> 		os.system( str( stuff[ i ] ) )
> 		print stuff[ j ]
> 		i += 1 ; j += 1
>
> The while loop does precisely what it should do: it runs the first  
> command using os.system(), and then prints out the string in the  
> second position of the list.
>
> Then I tried to do the same thing with a for loop that looks  
> logically equivalent.  I replaced the while loop with this for loop:
>
> 	# doesn't work
> 	for i in len( stuff ):
>   
Try this:
>   	for i in range(len(stuff)):
>
>
>   
> 		os.system( stuff[ i ] )
> 		j = i + 1
> 		print stuff[ j ]
>
> Python doesn't like it, though.  It gives me the following error:
>
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> TypeError: 'int' object is not iterable
>
> What precisely causes this error?  I come from a C background, and  
> while and for loops can be molded to do precisely the same thing; it  
> doesn't seem like this is the case in this scenario.
>
> Thoughts/ideas appreciated.  :)
>   
for expects, as the error says, an "iterable". range() provides an 
iterable. len() just gives an integer.

BTW I find it very hard to read code where there are spaces next to () 
and [].