Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 8: File Searcher App
Lecture: Recursion applied
Login or
purchase this course
to watch this video and the rest of the course contents.
0:01
Ok, let's see how recursion will us search not just the current directory that we give it
0:06
but the entire directory tree starting at the directory we provided as the root.
0:12
Here we have search folders, this is going to be our recursive function, and we are going to come here, we are going to list all the items here,
0:18
we want to for each item build up the full path to that item. Remember these little bits are just relative,
0:24
they are sort of the name but not including the path. Before we said we don't know what to do with directories
0:29
let's just get out of here and then we said if it is a file we will go get all the matching lines and information about that in extend to all matches,
0:37
well now we can use recursion to solve this problem so let's try this like else really quick, so we sort of put these in these two cases
0:45
so if it's a directory we do one thing otherwise, if it's a file we go search it. so what are we going to do,
0:51
we are just going to say if it's a directory, let's also search that directory and what method do we have that can search folders,
0:59
well, the one that we are in. But we are going to search a different folder, a subfolder, and the name of the subfolder is full item
1:05
and we still want to search for the same text, now this will come back with matches as well,
1:09
different sets of matches probably more, you never know, right, but it's all the stuff within that subfolder not just an individual file,
1:16
and then we'll say all matches.extent those matches as well. Look how perfectly recursion solves this problem
1:23
like it was really one or two lines of code, we removed the continue we just said search but a smaller subset of this tree
1:33
we want to go search and we are just going to recursively do that until there is no more directories we are just down to the end,
1:38
the end of that hierarchy if you will. So let's run this and see if it's working. So again, we are going to search our books,
1:44
now remember there is that classics folder that has Sherlock Holmes in it previously we did not have results for Sherlock Holmes
1:50
so hopefully we are going to search the books folder and within there we are also going to search the classics subfolder, let's give it a shot.
1:57
Again, we are going to search for Holmes, and here we go, wow, now we have a lot more results and we've got the Ulysses book
2:04
but we also have classics, The Adventures of Sherlock Holmes you can see on line 11587 the table had not been cleared yet, Sherlock Holmes had been...
2:14
beautiful, and you saw that recursion was the key to making this work in the most dramatically simple way possible. So in some sense our app is done,
2:25
if what we want to give our app is 10 books that are just all text and maybe that's a couple of megabytes
2:33
you can see that we can actually search that quite quickly and there is no problem,
2:37
but if the number of files and the quantity of files gets to be gigabytes of text
2:42
you'll see there is a severe performance problem especially around memory and we can do much better using some very cool features
2:50
called generator methods that's what we are going to do next.