Opening and Closing Files

Quick reference

• 00:04 In this video, I want to talk about opening and closing files and
• 00:07 when we looked at modules we're sort of opening a file, but not really.
• 00:11 We're importing a module into our program.
• 00:14 If you want to open an actual file or close a file,
• 00:17 it's a little bit different and that's what we're going to talk about.
• 00:19 So, first before we get started, let's create a second file, I'm going to right
• 00:22 click here and click here and click New File, and let's just call it names.text.
• 00:27 All right, so let's open this up, double click it, and
• 00:31 I'm just going to type some names, let's go John, Tim, Mary, and Bob.
• 00:36 So I'm going to save this, and so all we have here is just a simple text file,
• 00:40 any kind of file will work.
• 00:41 And we've got some stuff in the file.
• 00:43 So I'm going to close it.
• 00:44 Now let's say we want to open this file and do stuff with it from our Python file.
• 00:49 How would we do that?
• 00:50 Well, we need to create a file object.
• 00:52 And it's super easy to do with Python.
• 00:55 You just create a variable name like always.
• 00:58 Let's go my file.
• 01:00 Call it whatever you want, it doesn't really matter.
• 01:02 And then we type in open, this open function.
• 01:05 And then we need to pass it a few parameters.
• 01:07 So the first parameter is the name of the file.
• 01:10 So let's go names.txt.
• 01:13 And then separate each of these by a comma.
• 01:15 And then next we need to give it the open mode that we're going to use.
• 01:20 And I'll talk about that in just a second.
• 01:21 So I'm going to type in R.
• 01:23 And the third attribute is something called buffering and it's usually zero,
• 01:27 one or a number greater than one.
• 01:30 But we don't usually deal with buffering so
• 01:32 we're just going to sort of ignore that.
• 01:33 So here we have it and if we save this and run it of course nothing's going to
• 01:37 happen, because we've opened our file but we haven't actually done anything with it.
• 01:41 So before we talk about doing stuff with files and we'll do that a little bit later
• 01:45 on in the next couple of videos, I want to talk about this object.
• 01:48 We've created this file object.
• 01:50 There are a few attributes you can do to sort of play with this and
• 01:53 get information out of it.
• 01:55 Once you've opened it, you can find out the name of it.
• 01:58 So let's go print and say my_file.
• 02:01 And then .name.
• 02:03 So if we save this and
• 02:05 run it, we get names.txt because that's the name of our file.
• 02:08 So that's kind of cool, kind of a neat little thing you can do.
• 02:11 You can also say, has that file been closed yet?
• 02:14 We opened it but we didn't actually close it.
• 02:16 You always need to close your files once you open it.
• 02:18 May not remember if it's open or closed so we can type closed.
• 02:22 We save this and run it, we get false because it's not closed.
• 02:25 It's still open because we opened it right here.
• 02:27 And finally we can do the mode.
• 02:29 And I'm going to talk about modes in just a second.
• 02:31 We run this, we see R because that's the mode that I selected.
• 02:35 So I mentioned you can open these files.
• 02:37 You also always need to close them afterwards.
• 02:40 And it's really easy to close a file.
• 02:42 You just go, my_file.close(), and
• 02:44 then pass it, if you're doing the close function.
• 02:48 Then we save this.
• 02:49 Actually, let's take this, and let's change this to closed, save it and run it.
• 02:56 False, it's not been closed yet.
• 02:58 And now if we go like this, save it and run it, we're going to see it's true,
• 03:02 because this line closes the file.
• 03:04 Always at the end you want to sort of put your close statement there.
• 03:08 It's just, sort of, best practices.
• 03:09 Once your program ends, the file will close automatically.
• 03:12 But we want to get in the habit of closing files when we open them.
• 03:15 Very quickly now, I want to talk about this mode.
• 03:18 So what is a mode?
• 03:20 There are three main modes when opening files.
• 03:24 And I'll put these in the resource section.
• 03:28 You have r which is read only, w which is write only.
• 03:33 And a, which is appending.
• 03:35 Now in addition to that, we also have b, which stands for
• 03:39 binary, and plus, which stands for both reading and writing.
• 03:42 And we append these on to either of these three things.
• 03:46 So if you want to open read only in binary, you would do rb right.
• 03:52 If you want to do read only but also writing you would go r+.
• 03:56 If you want to write only but also read, w+.
• 04:00 If you want to write binary and also read, wb+.
• 04:04 So r is the default read only.
• 04:06 And what that does is,
• 04:07 when you open a file in read only mode, it means you can only read that file.
• 04:12 We could only read these names out of that file.
• 04:15 We couldn't save anything else onto the file.
• 04:17 We couldn't do anything with it.
• 04:18 We can just read it.
• 04:19 With write only you can't read it, but you can write stuff to it.
• 04:23 So, and you'll notice when you do that it overwrites the file.
• 04:26 If we called w on this file, names.txt, it would erase everything on there and
• 04:32 replace it with whatever we told it to put in there.
• 04:35 So you got to be careful about that.
• 04:36 With read only the pointer, which is,
• 04:38 think of the mouse, starts at the beginning of the file.
• 04:41 It starts up here and it reads everything down.
• 04:44 With append, the pointer goes at the end and
• 04:47 then you can add another name, right, Steve.
• 04:51 If you're going to append, you append it to the end.
• 04:54 So these are the different modes.
• 04:56 You use them whenever you open your file.
• 04:58 I usually tend to use r+, because then you can read and write.
• 05:02 So if I want to add something to the beginning of the file, if I want to put
• 05:05 a new name up here, I would do r+ because the pointer starts at the beginning.
• 05:10 If I wanted to put that name at the end like that, I would use a or
• 05:15 a+, because then the pointer goes at the end of the file.
• 05:18 So that's how you open a file.
• 05:19 That's how you close the file.
• 05:20 In the next video we'll look at actually reading stuff out of files and
• 05:24 writing things to files.

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