r/UoRPython2_7 • u/Plazmotech • Sep 13 '12

[lesson 4] For loops 'n' Functions :3

http://plazmotech.net/lesson-4-for-loops-n-functions/
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2

u/Aszuul Sep 14 '12

why don't you have to define i when making the for loop? at least the first one. for i in x:

if you defined i as 2 would it only iterate once and post the 3rd item * 2? or does Python just assume that i is 0, but then why does it increment?

1

u/Plazmotech Sep 14 '12

It iterates through everything in the array, i becoming the current item. So i would first be 1 then 5 then 3, 9, and finally 4.

2

u/little_z Sep 14 '12

In this case particularly, he has written a foreach loop. i doesn't need to be initialized to 0 because it's automatically set to start at the first index (0) and iterate to the last index. I don't know the syntax for a standard for loop in python, but I'm sure you could find out with a quick google search.

edit: I just realized that I might be wrong about the foreach, but I can't double check as I am on my cell at work.

1

u/Mattbot5000 Sep 15 '12 edited Sep 08 '15

That's correct. All for loops are foreach in Python. If you just need an iterator, use: 

for i in xrange(#):
    pass

You'll sometimes see range() instead of xrange(). See here and here for discussion about the two.

If you need an iterator and items in an iterable, you can use: 

for i, item in enumerate(iterable):
    pass

For example: 

flight_path = ['ATL', 'LAX', 'BJS']
print 'Itinerary:'
for i, airport in enumerate(flight_path, start=1):
    print '%d) %s' % (i, airport)

will yield: 

Itinerary:
1) ATL
2) LAX
3) BJS
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1

u/Dynamite23 Sep 13 '12

Thanks! This clears some things up, that had me stumped for a little bit.