Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 4: Journal app and file I/O
Lecture: Core concept: For-in loops

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0:00 We just saw the for-in loop in action.
0:03 And this is one of our core concepts from this application,
0:07 let's take a moment and dig into it more deeply.
0:09 Now for-in loops are the easiest and the safest way to process any collection.
0:14 It doesn't have to be just lists,
0:16 anything that is a collection can be used in one of these for-in loops.
0:20 So here we have an items list
0:22 it has three strings in it, 'cat', 'hat' and 'mat',
0:25 and we can go through those and print them out in order
0:28 just saying for item in items:
0:31 we can call item that variable anything we want
0:34 as long as it doesn't conflict with the existing other variables
0:37 and we just make that up on the spot as part of the loop
0:39 and then we could use it within the loop
0:42 so we say for item in items print() and then we just work with the item.
0:45 Now, that is what you will write most of the time,
0:48 but sometimes you want a number, an index,
0:50 a position associated with that item.
0:53 And when that is the case,
0:55 you wrap your collection in a call to enumerate
0:57 and you get back both an index, and an item, and you can work with those.
1:01 You can either grab it as a tuple or as I am doing in this particular example
1:05 I am projecting or unpacking that tuple,
1:09 into the two variables idx for index and item for the actual item.