1 00:00:05,360 --> 00:00:07,680 In this video, we'll have a look at the pop method. 2 00:00:09,840 --> 00:00:13,360 We've seen pop used with a dictionary, and it can also be used with a list. 3 00:00:14,240 --> 00:00:17,594 When popping items from a set, there's a slight difference. 4 00:00:17,760 --> 00:00:21,972 Sets aren't indexable, so the set pop method doesn't take any arguments. 5 00:00:22,160 --> 00:00:26,239 It pops an arbitrary item from the set, and returns that item. 6 00:00:28,640 --> 00:00:32,720 What do I mean by "arbitrary" item? I mean that you can't reliably predict 7 00:00:32,720 --> 00:00:36,800 which item will be popped from the set. You might get consistent behaviour, 8 00:00:36,800 --> 00:00:40,819 when popping integer values from a set, with some versions of Python. 9 00:00:40,880 --> 00:00:46,019 But if you run the same code on another Python version, you might get different values. 10 00:00:48,160 --> 00:00:51,920 You may think that getting "random" items from your set isn't much use. 11 00:00:51,920 --> 00:00:56,165 How can you write reliable code, if you don't know which value you'll be dealing with? 12 00:00:56,320 --> 00:00:59,611 In fact, you'll find that you often don't care. 13 00:01:01,760 --> 00:01:06,532 Imagine you're processing a set of tasks, and it doesn't matter what order they're performed. 14 00:01:06,640 --> 00:01:10,165 Popping them from a set would be fine, in that case. 15 00:01:10,165 --> 00:01:15,040 The pip module works like that. You can see a reference to it, in Martijn Pieter's answer 16 00:01:15,040 --> 00:01:20,431 to this stack overflow question. I'll switch to it in my browser. 17 00:01:24,240 --> 00:01:29,351 Read through it at your leisure. The link will be in the resources for this video. 18 00:01:31,120 --> 00:01:34,212 We're going to do something similar, in our example. 19 00:01:34,320 --> 00:01:38,480 We'll process each of the patients in our trial – from the previous video. 20 00:01:38,480 --> 00:01:42,080 We don't care what order we process them; as long as we process them all, 21 00:01:42,080 --> 00:01:47,040 and each one only gets processed once. Ok, let's go back to IntelliJ, 22 00:01:47,040 --> 00:01:50,160 and see pop in action. I've created a new Python 23 00:01:50,160 --> 00:01:55,792 file called prescription_processing.py - pause the video while you catch up. 24 00:01:56,080 --> 00:01:59,478 Start with the code to create the trial_patients set 25 00:02:18,720 --> 00:02:22,720 Our code is going to be fairly simple. As long as there are patients remaining in 26 00:02:22,720 --> 00:02:28,080 the trial_patients set, we'll loop, and process their prescription in some way. 27 00:02:28,080 --> 00:02:31,897 To do that, we'll loop, as long as the set isn't empty: 28 00:02:35,840 --> 00:02:40,195 Inside the loop, we'll pop a patient from the set, and print their name: 29 00:02:53,520 --> 00:02:56,000 Okay, run the program. 30 00:02:57,200 --> 00:03:01,406 It's not terribly exciting, we get the name of each patient printed out. 31 00:03:01,406 --> 00:03:04,916 Each time you run it, you'll probably get the names in a different order. 32 00:03:05,040 --> 00:03:09,776 That's what the documentation means by "Remove and return an arbitrary element from the set.". 33 00:03:09,840 --> 00:03:13,895 Sets have no ordering, remember! . So that's the pop method. 34 00:03:14,000 --> 00:03:18,323 It removes an item from the set, and returns it so that you can do something with it. 35 00:03:18,560 --> 00:03:23,644 We could, for example, use this code to send the patients' prescriptions to the pharmacy. 36 00:03:23,760 --> 00:03:28,800 I'll start by importing the patients dictionary, from the prescription_data file. 37 00:03:28,800 --> 00:03:30,825 I'll do that on line 1: 38 00:03:37,503 --> 00:03:43,284 Inside the loop, we can look up the patient's prescription in the dictionary. 39 00:04:03,870 --> 00:04:07,632 Each time we run the program, which I'll do now: 40 00:04:08,400 --> 00:04:12,628 we get the patient names, and their prescriptions, printed out. 41 00:04:12,880 --> 00:04:16,720 Elsewhere in the code, we might be adding more patients to the trial. 42 00:04:16,720 --> 00:04:20,959 This code ensures that we don't produce prescriptions for the same patient again. 43 00:04:20,959 --> 00:04:24,320 They're removed from the set, and won't be processed again. 44 00:04:24,320 --> 00:04:29,260 That's the technique used in the distlib library, mentioned in that stack overflow post. 45 00:04:29,360 --> 00:04:33,376 pop probably isn't something you'll use very often, but it's there when you need it. 46 00:04:33,520 --> 00:04:41,440 Alright, in the next video, we'll start to look at the set operations. See you in the next video.