1 00:00:00,000 --> 00:00:03,990 The Python standard library has a number of modules that you can import into 2 00:00:04,000 --> 00:00:06,990 your programs and use for your own purposes. 3 00:00:07,000 --> 00:00:12,990 This page has a list of them starting here in section 7, under String Services. 4 00:00:13,000 --> 00:00:15,990 And you'll see that there are quite a few of them. 5 00:00:16,000 --> 00:00:19,990 So we're going to just go through a few of these, a few of the more common 6 00:00:20,000 --> 00:00:22,990 ones and show you as an example how you can use them. 7 00:00:23,000 --> 00:00:29,990 And I suggest that you go through this list at least once and just look out what they are. 8 00:00:30,000 --> 00:00:30,990 And just look at their descriptions. 9 00:00:31,000 --> 00:00:33,990 Just read through the list, so you have an idea of the kinds of things that 10 00:00:34,000 --> 00:00:35,990 are available to you. 11 00:00:36,000 --> 00:00:40,990 So here in Eclipse, we're going to make a working copy of modules.py. 12 00:00:41,000 --> 00:00:46,990 Call this modules-working.py, and we'll open that up. 13 00:00:47,000 --> 00:00:52,990 You'll notice that here we're importing sys, and here on the web page you'll see 14 00:00:53,000 --> 00:00:57,990 sys is for system-specific parameters and functions. 15 00:00:58,000 --> 00:01:03,990 If we open that page, you'll see that there's full documentation on all of the 16 00:01:04,000 --> 00:01:05,990 things that you can do with sys. 17 00:01:06,000 --> 00:01:08,990 So, one of these is to get the Python version. 18 00:01:09,000 --> 00:01:10,990 This is with sys version info. 19 00:01:11,000 --> 00:01:19,990 And so if we run this, you'll see that we say, this is Python version 3.1.2. 20 00:01:20,000 --> 00:01:22,990 You can also get the system platform. 21 00:01:23,000 --> 00:01:30,990 You can say print(sys.platform) and if we save that and run it, you'll see 22 00:01:31,000 --> 00:01:32,990 that this is win32. 23 00:01:33,000 --> 00:01:38,990 On my Mac at home it says Darwin and whatever operating system you're running Python on, 24 00:01:39,000 --> 00:01:40,990 it will give you an idea. 25 00:01:41,000 --> 00:01:42,990 And this is a category of operating system. 26 00:01:43,000 --> 00:01:44,990 It's not actually the operating system. 27 00:01:45,000 --> 00:01:48,990 You can get the operating system from the OS module, but this gives you an 28 00:01:49,000 --> 00:01:53,990 indicator of what types of services are going to be available on this platform. 29 00:01:54,000 --> 00:01:57,990 Like, for instance, if I'm on a win32 platform, I'm not going to do things that 30 00:01:58,000 --> 00:02:00,990 are UNIX specific and vise-versa. 31 00:02:01,000 --> 00:02:03,990 So, that can be a useful token to see. 32 00:02:04,000 --> 00:02:09,990 If we import OS, this is another module that you'll find in that list, 33 00:02:10,000 --> 00:02:13,990 you'll notice that I can import inside of the function. 34 00:02:14,000 --> 00:02:15,990 I don't need to do my import at the top. 35 00:02:16,000 --> 00:02:19,990 This allows me to actually selectively import things, say I read that 36 00:02:20,000 --> 00:02:24,990 sys.platform variable and say I'm going to do certain things one way or 37 00:02:25,000 --> 00:02:27,990 certain things another way depending on which platform I get. 38 00:02:28,000 --> 00:02:33,990 So I can import modules selectively, and the system won't try to import them if 39 00:02:34,000 --> 00:02:36,990 they're not on the right platform or whatever. 40 00:02:37,000 --> 00:02:44,990 So, here we can get the os.name for example, and if I save that and run it, 41 00:02:45,000 --> 00:02:47,990 you'll see this says nt. 42 00:02:48,000 --> 00:02:50,990 So, that's the name that it's giving this particular type of Windows. 43 00:02:51,000 --> 00:02:55,990 And it distinguishes it like from, for example the older Windows 3 or 44 00:02:56,000 --> 00:02:58,990 something like that. 45 00:02:59,000 --> 00:02:59,990 I can get variables from the environment. 46 00:03:00,000 --> 00:03:05,990 I can print os.getenv and say I want the PATH variable. 47 00:03:06,000 --> 00:03:10,990 Save and run. 48 00:03:11,000 --> 00:03:15,990 And there is the PATH variable from the operating system. 49 00:03:16,000 --> 00:03:24,990 So, I can get current working directory, and we'll save and run that. 50 00:03:25,000 --> 00:03:26,990 And there is the current working directory. 51 00:03:27,000 --> 00:03:31,990 Of course, this module has a lot of functions in it. 52 00:03:32,000 --> 00:03:34,990 Just one more I want to show is the urandom function. 53 00:03:35,000 --> 00:03:38,990 This is sometimes useful. 54 00:03:39,000 --> 00:03:41,990 Save and run that. 55 00:03:42,000 --> 00:03:44,990 This is a function that'll give a string of random bytes. 56 00:03:45,000 --> 00:03:54,990 And of course you see that this is the byte type, and I set 25 so it's 25 bytes long. 57 00:03:55,000 --> 00:04:01,990 Another useful module is the urllib module, and we'll go ahead and import from 58 00:04:02,000 --> 00:04:10,990 that urllib.request, and we'll grab a web page from the internet. 59 00:04:11,000 --> 00:04:19,990 urllib.request.urlopen, and we'll give it a URL here. 60 00:04:20,000 --> 00:04:25,990 We'll go ahead and get my homepage, print(page). There we go. 61 00:04:26,000 --> 00:04:28,990 Save that and run it. 62 00:04:29,000 --> 00:04:30,990 We get this object. 63 00:04:31,000 --> 00:04:32,990 And that's an iterable object. 64 00:04:33,000 --> 00:04:38,990 So, we can iterate on it and say for line in page: 65 00:04:39,000 --> 00:04:46,990 print, and convert each line to a string because they come out binary, and 66 00:04:47,000 --> 00:04:49,990 we provide an encoding. 67 00:04:50,000 --> 00:04:51,990 And they have no lines at the end of them. 68 00:04:52,000 --> 00:04:55,990 So we'll give it this line ending there. 69 00:04:56,000 --> 00:05:06,990 And we save and run and there is an entire web page. 70 00:05:07,000 --> 00:05:08,990 So, that's a really useful one. 71 00:05:09,000 --> 00:05:12,990 There are a lot of very useful modules in here. I'm just going to take a quick look 72 00:05:13,000 --> 00:05:13,990 at a couple of more. 73 00:05:14,000 --> 00:05:16,990 One is the random module. 74 00:05:17,000 --> 00:05:18,990 It's a very rich random number library. 75 00:05:19,000 --> 00:05:32,990 For example, you can print a random number from in a range. randint, 76 00:05:33,000 --> 00:05:36,990 A range between 1 and 1000. Save and run. 77 00:05:37,000 --> 00:05:37,990 And then we have the number 726. 78 00:05:38,000 --> 00:05:41,990 If we run it again, we get a different number and a different number and 79 00:05:42,000 --> 00:05:42,990 a different number. 80 00:05:43,000 --> 00:05:44,990 And that's very useful. 81 00:05:45,000 --> 00:05:51,990 Another very useful method in this library is the shuffle method. It takes a list. 82 00:05:52,000 --> 00:05:56,990 I'm going to just give it a list with a range in it, and if we print that list, 83 00:05:57,000 --> 00:06:02,990 you'll see that we have a range of 25 numbers. 84 00:06:03,000 --> 00:06:15,990 We can shuffle the list, random.shuffle, and print it again. 85 00:06:16,000 --> 00:06:19,990 And there we have the list shuffled randomly. 86 00:06:20,000 --> 00:06:25,990 If we do that a few times, save and run, you can see we get different 87 00:06:26,000 --> 00:06:28,990 shuffles each time. 88 00:06:29,000 --> 00:06:33,990 Finally, in our little partial tour of the standard library, look at 89 00:06:34,000 --> 00:06:46,990 the datetime module. 90 00:06:47,000 --> 00:06:53,990 So we'll save that and run it, and there we have the time as of right now 91 00:06:54,000 --> 00:06:54,990 when I'm recording this. 92 00:06:55,000 --> 00:07:12,990 In fact, we can do this. now.year, now.month, now.day, now.hour, now.minute, 93 00:07:13,000 --> 00:07:20,990 now.second and now.microsecond, and save that and run it. 94 00:07:21,000 --> 00:07:24,990 And there we have all of those components, separately usable with these 95 00:07:25,000 --> 00:07:26,990 properties of the datetime object. 96 00:07:27,000 --> 00:07:30,990 So, these are just a few of the standard modules that are available with Python. 97 00:07:31,000 --> 00:07:34,990 Again I strongly recommend that you look through the documentation for these 98 00:07:35,000 --> 00:07:38,990 standard modules. At least read their descriptions so that you get an idea of 99 00:07:39,000 --> 00:07:42,990 what's available there, so that as you're going through writing your own code, 100 00:07:43,000 --> 00:07:44,990 you're not tempted to reinvent the wheel. 101 00:07:45,000 --> 00:07:48,990 The modules that are included with Python and the Python distribution tend to 102 00:07:49,000 --> 00:07:49,990 be very well written. 103 00:07:50,000 --> 00:07:55,990 They tend to be very feature rich and they tend to be quite well optimized and reliable. 104 00:07:56,000 --> 00:08:06,000 So, I suggest that you use them when you have an opportunity.