On Sep 28, 2007, at 10:59 AM, bob gailer wrote: > 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.
Great! I was under the impression that the range was implied, but I guess not. ;) > BTW I find it very hard to read code where there are spaces next to > () and []. I find it difficult to read code where there *aren't* spaces next to the () and [] and there are several parenthesis/brackets next to each other. :) Personal preference. Thanks again. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
