1 00:00:00,000 --> 00:00:04,990 Dictionaries are Python's version of associative arrays or hashed arrays. 2 00:00:05,000 --> 00:00:07,990 Dictionaries are created in a couple of different ways. 3 00:00:08,000 --> 00:00:23,990 We can create a dictionary with the curly braces and we can say key value like this. 4 00:00:24,000 --> 00:00:26,990 So now, we have a dictionary with those values in it. 5 00:00:27,000 --> 00:00:30,990 Actually, an easier way to create dictionaries is with its constructor because 6 00:00:31,000 --> 00:00:35,990 this allows you to use the named parameters feature of Python and it's just a 7 00:00:36,000 --> 00:00:36,990 whole lot easier to type. 8 00:00:37,000 --> 00:00:45,990 So you will see it done this way more often. 9 00:00:46,000 --> 00:00:53,990 We get exactly the same result and see that that type is a class dictionary. 10 00:00:54,000 --> 00:00:58,990 Finally, if you want to, you can even initialize one dictionary from another. 11 00:00:59,000 --> 00:01:10,990 If I have another dictionary? 12 00:01:11,000 --> 00:01:13,990 And so there I have that dictionary. I can say d = 13 00:01:14,000 --> 00:01:20,990 dictionary and I can take these definitions from up here, copy those and paste 14 00:01:21,000 --> 00:01:25,990 those in, and then I can actually specify that other dictionary with the two 15 00:01:26,000 --> 00:01:30,990 asterisk notation and I get a dictionary that has all of that in it. 16 00:01:31,000 --> 00:01:38,990 You can test if a value is in a dictionary by saying 'four' in x and I see that 17 00:01:39,000 --> 00:01:45,990 that's True and if I say 'three' in x that will not be true, because x here has 18 00:01:46,000 --> 00:01:47,990 just four, five and six in it. 19 00:01:48,000 --> 00:01:50,990 Likewise, you can iterate over a dictionary. 20 00:01:51,000 --> 00:01:53,990 You can say four k in d: 21 00:01:54,000 --> 00:01:58,990 print (k) and that will print out all of the keys. 22 00:01:59,000 --> 00:02:11,990 If you want to, you can say for k key and value in d.items print k and value. 23 00:02:12,000 --> 00:02:15,990 And that will give you both the keys and the values all in one fell swoop. 24 00:02:16,000 --> 00:02:20,990 If you want to find a particular item in a dictionary, one way to do it is to 25 00:02:21,000 --> 00:02:24,990 simply subscript it. 26 00:02:25,000 --> 00:02:28,990 The problem with that is that if your dictionary does not have that key, you 27 00:02:29,000 --> 00:02:29,990 will get an exception. 28 00:02:30,000 --> 00:02:34,990 If I try x sub 'three', I will get an exception. 29 00:02:35,000 --> 00:02:38,990 The way around that is to use the get method. 30 00:02:39,000 --> 00:02:45,990 If I say x.get('three'), it will simply silently give me the none value. 31 00:02:46,000 --> 00:02:51,990 If I say d.get('three') then I get the value. 32 00:02:52,000 --> 00:02:56,990 Another benefit of this is using the get method I can give it a default 33 00:02:57,000 --> 00:03:06,990 value. I can say give me that value of three or give me some default value. 34 00:03:07,000 --> 00:03:07,990 And I get the default value. 35 00:03:08,000 --> 00:03:10,990 Here I typed in the text 'not found'. 36 00:03:11,000 --> 00:03:15,990 If I simply want to delete an item from a dictionary, I can just look at the x here. 37 00:03:16,000 --> 00:03:17,990 I've got those items there. 38 00:03:18,000 --> 00:03:29,990 I can say del x' sub four' and now that's gone or I can say x.pop('five') and it will 39 00:03:30,000 --> 00:03:33,990 give me the value and delete it at the same time. 40 00:03:34,000 --> 00:03:34,990 So those are the major functions of dictionaries. 41 00:03:35,000 --> 00:03:37,990 Dictionaries are tremendously useful. 42 00:03:38,000 --> 00:03:43,990 Whenever you need to organize your data in such a way that it's easy to find, 43 00:03:44,000 --> 00:03:47,990 you can certainly store any kind of data in a list or in a tuple. 44 00:03:48,000 --> 00:03:50,990 But the indexes are always going to be numeric. 45 00:03:51,000 --> 00:03:53,990 The advantage of the dictionaries is that the indexes are data. 46 00:03:54,000 --> 00:03:57,990 So you can index it on any kind of data. 47 00:03:58,000 --> 00:04:02,990 Usually, you will use text, usually you will use words, but this allows you to 48 00:04:03,000 --> 00:04:06,990 basically create your own named spaces and organize them. 49 00:04:07,000 --> 00:04:07,990 They can be hierarchical. 50 00:04:08,000 --> 00:04:11,990 You can store dictionaries within dictionaries, you can store lists and tuples 51 00:04:12,000 --> 00:04:16,990 within dictionaries, and you will find as you will look through the examples 52 00:04:17,000 --> 00:04:20,990 of the code that I have written, I will often times carry one dictionary in a 53 00:04:21,000 --> 00:04:26,990 global namespace and put all of my data inside of that and then it becomes manageable. 54 00:04:27,000 --> 00:04:31,990 It's like a halfway point between flat data and an object with methods. 55 00:04:32,000 --> 00:04:34,990 Obviously, there is going to be times you are going to want to create an 56 00:04:35,000 --> 00:04:38,990 object with methods to handle your data in very specific ways, but for just 57 00:04:39,000 --> 00:04:42,990 organizing a whole lot of global variables or flags, you will find that 58 00:04:43,000 --> 00:04:48,990 dictionaries are very useful and for organizing object data within an object, 59 00:04:49,000 --> 00:04:51,990 you will find that dictionaries are very, very useful and very, very commonly 60 00:04:52,000 --> 00:05:02,000 used in these kinds of situations.