Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 8: File Searcher App
Lecture: Core concept: Generator methods
0:00 Let's look at this core concept of generator methods.
0:03 Here we have a Fibonacci method and we are passing the limit to it,
0:08 to say how many numbers do we want,
0:10 in traditional type of methods you could have a list and we could go through
0:14 and compute all the items adding them to the list and then
0:17 when all the answers are done, the entire lists are generated,
0:20 we could then return that list.
0:23 Generator methods provide us a different mechanism,
0:26 a different way to do that, it dramatically different performance characteristics.
0:30 Here what we do is we come to this method and we work our way down
0:34 just like any regular method until we get to the yield keyword,
0:37 and the yield keyword says here is an item in our collection,
0:39 and immediately this method is sort of suspended,
0:43 the item is returned to whoever called this function as the next item in the sequence,
0:48 they can process it and either decide to continue pulling on the sequence from
0:52 like a foreign loop or something or they can stop and that's it,
0:56 you've only computed one item.
0:57 But if they come back and they ask for the next one
0:59 then execution will resume right here, and it just goes around, gives the item back,
1:04 the caller looks at it and it gives you this kind of lazy evaluation of items
1:09 that ultimately turn into sequences where the sequences don't have to be stored
1:14 in memory all at once before you get to work with them,
1:17 so these generator methods and this yield keyword are really powerful
1:21 when you are processing large sets of data in series
1:24 or you are even building pipelines where one step pulls on some large data source
1:28 and then another step takes that process transformed,
1:31 filtered a bit and does more work on it and then you keep doing that
1:34 and passing along until finally some sort of pipeline spits out
1:38 a smaller transformed set of items,
1:40 the composition of generator methods is amazing there.
1:43 And that's what we are going to build in our file searcher app, when we get back to it.