Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 8: File Searcher App
Lecture: Searching single files
0:01 Ok, let's implement the actual search.
0:03 The first thing that we need to do is actually go to this folder and find all the files.
0:08 So again, our friend OS will help.
0:10 We can say OS.list.dir and give it a folder,
0:14 and here this is going to return all of the items in here so let's say items,
0:18 notice I am not calling them files because
0:21 sometimes they are folders, sometimes they are files.
0:24 So, we are going to do our loop,
0:27 we are going to say for item in items and we want to check,
0:29 well if this is a folder we don't want to do this so we'll say if os.path.isdir item
0:36 we are going to not process this item but we want to keep going to the loop
0:40 and the perfect keyword for that is continue,
0:43 so basically go back to the top of the loop,
0:46 pull another item and keep going.
0:48 If it's not a directory, it has to be a file,
0:50 so then let's write a method that will just search the file,
0:53 so what we need to do is store the results, the matches somewhere
0:56 so we'll just say matches = search single file
0:59 and we'll give it the file and the text to search.
1:03 Now, one thing that we are going to want to be careful with
1:06 is when we say listdir this only gives us the file name,
1:09 not the full path name so either way whether it's a directory or a file,
1:13 we need to do something like this,
1:15 we'll go full item = os.path.join and remember,
1:21 we made sure that this is an absolute path
1:24 and then we want to join up the subitem, perfect,
1:26 so here we got the check full item
1:29 and down here we are going to pass full item,
1:32 somehow we are going to- we'll get the search method in a minute,
1:34 somehow we got to do something with these and that's going to be
1:36 like a collection of some sorts, so let's say all matches,
1:41 initially it's an empty list and I'm going to put some stuff into it
1:45 in the end we will return all matches,
1:46 so here we are going to say something like this,
1:48 if this was one item we would say append,
1:51 but if it's a collection we want to add the items from that collection individually here
1:55 which is what we want, we'll say extend matches.
1:58 Cool, so last bit to make this work for round one is to implement this file,
2:05 so now we know this is a full path to a file name
2:08 so we'll just go with that
2:10 and here let's be a little more clear we'll call this search text.
2:13 The first thing to do is open the file so we'll just use our little context manager
2:17 to make sure we close it under all circumstances
2:19 we'll say file name read only and let's treat this as text,
2:22 you'll see there are potential problems when we get into things like binary file,
2:26 so if I give it a folder and it just starts go through all of the subfolders,
2:29 what if there is like images in there or something,
2:31 then we want to just go through each line in the file
2:33 and check it to see if the search text appears in it,
2:38 so it turns out that these file streams are iterable
2:41 so I could say for line in fin and in a really nice way
2:45 just sort of smoothly stream over them without loading the whole file of them
2:50 in the memory as like an array of strings or something like this,
2:52 this is also going to be really key way to use these generator methods later on
2:56 but we are not there yet.
2:58 So the first question is we want to search to see
3:00 if this substring is in the line and we probably don't care about case sensitivity,
3:05 or things like that,
3:06 so let's say if line.find- there is two ways to look for substirng,
3:11 I could say index or I could say find,
3:14 if I ask for the index and it doesn't exist it will actually throw an exception, but find,
3:19 we'll just turn negative one if it's not found,
3:22 so I'll search for search text and before we do
3:25 we want to create a lower case version of that string,
3:27 we'll say if the return value is greater or equal to zero
3:31 so they actually found find found the substring.
3:35 The other thing we got to do is make sure that this is lower case,
3:38 we could do that once above here instead of every time we had a file,
3:44 so let's do something like return text.lower.
3:47 Cool, so if this is the case let's for now just somehow collect up this line of text,
3:53 we are going to see that this is not the ideal way to do this
3:55 and we'll fix it just in a moment,
3:57 but let's come over here and create a little submatches,
3:59 matches just for this file, and that's the case we'll say append and we'll just,
4:05 for now this is not the final answer,
4:07 we'll just append the line of text that we are going to match.
4:11 And in the end we'll return matches.
4:14 So a very limited version of our search is I think working,
4:19 let's give it a test so we want to come to create a list to store all of our matches,
4:22 we are going to get all of the directories and files in the current folder,
4:28 we'll go to them, we'll build up the full path which is to join the full path
4:33 with just the names of the subitems,
4:35 then we'll see if it's a directory for now we are going to skip it,
4:37 if it's a file we'll search it and if there is a match,
4:40 we'll add those in there if it's empty then it will just have no effect.
4:43 Awesome, let's go and try to run this.
4:45 So on my desktop I actually have some files here that we are going to go search,
4:49 and let's see, if we go to some classics like you can see we have Dracula,
4:53 The Adventures of Sherlock Holmes, things like that,
4:56 now this is the full text of the Sherlock Holmes book
4:59 and I got this from Project Gutenberg and there is a bunch of other ones,
5:03 we'll go through in a little bit, but these are actually the full files
5:06 so you'll see this is 160Kb that's 777 Kb of text that is a beast of a book,
5:14 Ulysses is 1.5 Mb, so we are going to go through all of these files here,
5:20 notice we are not going to get into the classics yet,
5:23 because we are just looking at the files.
5:26 We are skipping a case where it's a directory,
5:29 so let's go and search here, right,
5:31 so we are going to search that books folder which is full of those text books
5:36 and the phrase we want to search for is let's say "friends",
5:42 we'll that's pretty fantastic,
5:43 except for we forgot to print out the results, let's do that really quick.
5:53 Ok, so we'll capture the matches and for each one int here we'll just print this out.
5:56 Try again.
5:57 Search for friends and you can see we found some results, look at that.
6:02 So we went through all the various text files and we have printed them out,
6:05 now this is not a very helpful answer,
6:07 but at least you can see that it's working.
6:11 Let's just do a little bit of a sanity check,
6:16 "And Harry of the six wives' daughters and the lady friends from-"
6:17 "Your friends are inside,"
6:19 remember, we are just doing substrings, so friends,
6:21 if we had searched for friend it would also find friends,
6:23 we are not doing anything fancy it's just substring,
6:26 but it does look like it's working,
6:28 now what line in what book did that appear in?
6:31 I have no idea, so our next job is to fix that so we actually return
6:35 more information about our search.