Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 6: LOLCat Factory
Lecture: Downloading and writing binary data

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0:00 Now that we have this data downloaded form the internet,
0:03 let's go and write it to our file.
0:05 We want to save this data to a particular name
0:08 related to the cat name in the folder that we pass
0:11 so this should be pretty easy to write,
0:13 we'll say save image and we'll give it the folder
0:16 we'll give it the name and the data.
0:20 So down here we are going to have a method like so
0:23 now you worked with files before and you know
0:26 when you are just going to use the file stream just for a moment
0:29 and then you are going to close it right away
0:32 you want to use what is called a context manager
0:34 so we'll say with and open() is how we get all the file stream,
0:37 and we want to give it a name so let's come up here
0:39 and say file name = and again, we are going to use the os model
0:42 so we'll say os and import that at the top,
0:46 we'll say path.join() and our folder is in absolute path so that should work
0:51 and then we have our name and then this is like the name of the cat
0:55 like lol cat 1 lol cat 7, these are basically jpg's
0:58 so let's just add on the file extension.jpg.
1:02 So now we can say open file name and say as fout for output file stream,
1:07 and then we are going to somehow work with this,
1:09 if I were to just write this code and try to write this data to it,
1:14 this data is binary, this by default is a text file
1:18 it's not going to turn out so well for us
1:21 so what we need to do is go over here and change the mode,
1:23 and we can say I'd like to write, by default it's read only
1:27 and I'd like to write not just text but binary
1:30 so we'll set the mode to wb for write binary
1:32 and then I could work with the output stream
1:35 and the data stream and sort of copy those around
1:37 and juggle the bytes and that would be fine
1:40 but it turn out there is a module called shell util that will help us out here.
1:45 So we'll say shutil, like so and we want to import that at the top of course,
1:50 and it has a method called copy file object.
1:54 So we can say I would like to copy this data stream to that data stream,
1:59 done, one line, beautiful.
2:01 Now, PyCharm says you should really move your method down one line,
2:04 according to pep 8 so there we go.
2:07 All right, we are ready to run this app and get some cats
2:09 but remember I told you on line 14, 15 here we are doing it wrong
2:14 so let me run it, get some sort of not working images,
2:18 and then I'll show you how to fix it, it's really easy but it's also easy to overlook.
2:22 Let's make sure we get some output while we are running our download
2:26 so we'll do a little print statement here,
2:28 we'll say contacting server to download cats,
2:33 and we'll say something like print downloading cat
2:40 and then let's actually involve the name here,
2:44 I'm going to say plus name,
2:46 and then at the very end I guess we could print done,
2:49 something like so so let's run it.
2:56 Ok, how exciting, let's go look at our cats,
2:58 so now you can see we have all of our cats and if I open them up,
3:02 that's not a super cool cat,
3:04 I love all cats and I was hoping for a good little laugh when I saw this picture,
3:08 and this made me sad,
3:10 well you might think there is a problem with PyCharm
3:12 but in fact, if we actually open this up and find her you would see
3:15 there is not really a proper picture there,
3:17 so let's go back here and talk about the mistake
3:19 we made when downloading binary data using requests
3:22 so in order to work with this raw stream here
3:24 in the manner that we were doing it,
3:27 we need to go tell request to operate in what is called streaming mode,
3:30 so we can say stream = true, and now if we just rerun it
3:33 you should see some nice cats.
3:37 Ok, it's all done, let's go look at the cats.
3:41 Nice, trash cat is not amused, but I am, because this is awesome,
3:45 let's look at one more, uuu I'm in your quantum box, maybe.
3:48 Ok, so perfect, we've downloaded our data using requests
3:52 and we are working with the raw stream
3:55 and we set stream mode to be true
3:57 we then pass that stream over to our saved image
4:00 which we create a binary file we can write to
4:03 and we use the shell utility copy file object to copy from this stream to that stream.
4:10 But as a user, how would I know my cats have been downloaded
4:13 other than seeing done, ok, great, done,
4:15 but I actually want to see the cats
4:17 so the next thing we are going to do is show the cats to the user.