1 00:00:02,280 --> 00:00:07,620 Hey, let's run a few code experiments now for a better understanding of functions. 2 00:00:07,860 --> 00:00:13,860 Specifically, you want to understand the difference between function definitions and function calls. 3 00:00:13,950 --> 00:00:19,420 And that is what the first experiment is about, the difference between function calls and definitions. 4 00:00:19,440 --> 00:00:27,480 So if I remove all these calls here and I just leave the function there and I run the codes, nothing 5 00:00:27,480 --> 00:00:29,340 will be returned as an output. 6 00:00:30,770 --> 00:00:33,620 Well, you could say there is no print function here. 7 00:00:33,620 --> 00:00:35,960 That's why we didn't get any outputs. 8 00:00:36,230 --> 00:00:39,140 But I can provide a print function here. 9 00:00:39,380 --> 00:00:41,150 Let's say, Hey, hey. 10 00:00:42,440 --> 00:00:44,360 And I run the code again. 11 00:00:44,360 --> 00:00:45,410 No outputs. 12 00:00:46,550 --> 00:00:48,020 So why is that? 13 00:00:48,110 --> 00:00:53,930 Well, that's because this is just a recipe of the process. 14 00:00:55,160 --> 00:00:58,880 If we wanted to use our coffee making example again. 15 00:00:59,480 --> 00:01:08,090 So when you go to order a coffee in a bar and you go to the bartender and you ask them, I want a coffee. 16 00:01:09,000 --> 00:01:11,160 They have a recipe in mind. 17 00:01:11,160 --> 00:01:13,980 Maybe in their mind, maybe they have written it somewhere. 18 00:01:14,160 --> 00:01:17,520 So the recipe is the function definition. 19 00:01:17,520 --> 00:01:19,450 That's the function definition. 20 00:01:19,470 --> 00:01:24,960 The recipe itself has to be executed by someone. 21 00:01:24,990 --> 00:01:26,160 The bartender. 22 00:01:27,230 --> 00:01:34,130 So the function also has to be executed in order to get the output and we execute the function like 23 00:01:34,130 --> 00:01:34,670 this. 24 00:01:34,670 --> 00:01:36,050 So greet. 25 00:01:40,000 --> 00:01:42,640 So that's the variable and that's the value. 26 00:01:43,680 --> 00:01:51,810 So at this point this will be equal to Halo with first letter capitalized. 27 00:01:53,370 --> 00:01:57,780 But if we run this again, what we get is, hey, hey. 28 00:01:58,170 --> 00:02:01,980 So the function was called and that proves it. 29 00:02:02,010 --> 00:02:03,030 We get hey, hey. 30 00:02:03,030 --> 00:02:06,270 So the function was called because this was executed. 31 00:02:06,510 --> 00:02:08,590 That's how we know the function was called. 32 00:02:08,610 --> 00:02:15,480 We don't get Halo printed out because we simply got a low and we stored it in greetings. 33 00:02:15,480 --> 00:02:21,450 So if we want hello to be print out, we say print greeting. 34 00:02:22,080 --> 00:02:24,840 You run again the code and then you get say hey. 35 00:02:24,840 --> 00:02:26,010 And also hello. 36 00:02:27,400 --> 00:02:35,110 So it's very important to realize that the function call is equal to a value. 37 00:02:35,140 --> 00:02:40,000 The value of that is always whatever is returned in here. 38 00:02:40,630 --> 00:02:43,210 So it could be a string, it could be a number. 39 00:02:44,310 --> 00:02:48,750 It could be any object that the function returns. 40 00:02:50,330 --> 00:02:55,250 So I hope that helps you understand the difference between the function definition and the function 41 00:02:55,250 --> 00:02:55,820 call. 42 00:02:56,270 --> 00:03:01,370 Now, the next experiment, it is about the return statement. 43 00:03:01,460 --> 00:03:06,290 So try to remove that line and print out the code. 44 00:03:09,470 --> 00:03:11,150 This is what we get this time. 45 00:03:11,840 --> 00:03:12,130 Hey. 46 00:03:12,130 --> 00:03:12,400 Hey. 47 00:03:12,410 --> 00:03:13,210 And none. 48 00:03:13,220 --> 00:03:17,900 So again, the interpreter goes and executes the blueprints. 49 00:03:17,930 --> 00:03:19,490 It doesn't do anything. 50 00:03:19,760 --> 00:03:21,890 It just looks at the recipe. 51 00:03:22,770 --> 00:03:24,740 And then you execute the recipe here. 52 00:03:25,560 --> 00:03:32,310 But the problem is that this time the recipe has not instructed what to return. 53 00:03:32,940 --> 00:03:41,220 So the coffee was prepared, but the recipe didn't say, Oh, give that coffee to. 54 00:03:41,970 --> 00:03:43,020 The client. 55 00:03:45,260 --> 00:03:53,740 And when that doesn't happen implicitly, the function definition will return a non object. 56 00:03:53,750 --> 00:03:59,210 So just like we have integer strings, we also have this special object called None. 57 00:03:59,930 --> 00:04:03,800 None is basically to represent nothing. 58 00:04:05,560 --> 00:04:11,310 So in Python, you can actually in the console you can just say none. 59 00:04:11,320 --> 00:04:14,710 So that's recognized as a value. 60 00:04:15,190 --> 00:04:18,550 So it's not a string, it doesn't have quotes. 61 00:04:18,550 --> 00:04:21,459 So this would be different from that. 62 00:04:22,270 --> 00:04:23,140 That is a string. 63 00:04:23,140 --> 00:04:25,210 That is a special object. 64 00:04:25,660 --> 00:04:29,920 So that's here is equivalent of having return none. 65 00:04:30,310 --> 00:04:32,880 If we run this, we're going to get the same error. 66 00:04:32,920 --> 00:04:35,460 Hey, sorry, the same output. 67 00:04:35,470 --> 00:04:36,430 It's not an error. 68 00:04:36,460 --> 00:04:37,180 The same. 69 00:04:38,080 --> 00:04:38,320 Hey. 70 00:04:38,320 --> 00:04:38,650 Hey. 71 00:04:38,650 --> 00:04:39,730 And none. 72 00:04:42,800 --> 00:04:48,680 So you normally want to return something here in this case is new message. 73 00:04:49,920 --> 00:04:56,640 Some people what they will do, especially beginners, they will confuse print with return. 74 00:04:56,640 --> 00:05:03,180 So instead of returning something, they will say a print new message and let's see what we get this 75 00:05:03,180 --> 00:05:03,720 time. 76 00:05:05,350 --> 00:05:06,010 So. 77 00:05:08,610 --> 00:05:09,810 This is what happens. 78 00:05:09,990 --> 00:05:13,860 The interpreter reads the recipe and then it executes the recipe. 79 00:05:13,860 --> 00:05:22,020 So messages associated to the hello string and the new message is associated to hello with the first 80 00:05:22,020 --> 00:05:23,180 letter capitalized. 81 00:05:23,190 --> 00:05:25,560 So far, so good than print. 82 00:05:25,590 --> 00:05:30,300 Hey, so this is printed out in here then Print message. 83 00:05:30,870 --> 00:05:32,190 Message is printed out. 84 00:05:32,220 --> 00:05:32,970 Hello. 85 00:05:34,890 --> 00:05:36,720 You see with the letter cabinet lights. 86 00:05:36,720 --> 00:05:38,160 So, so far, so good. 87 00:05:38,280 --> 00:05:40,010 And then none is printed out. 88 00:05:40,020 --> 00:05:41,880 Why is not printed out? 89 00:05:41,910 --> 00:05:49,440 Well, because I just told you that when you don't have that return statement, the function will always 90 00:05:49,440 --> 00:05:51,210 return none. 91 00:05:51,570 --> 00:05:54,870 So implicitly, the function again is doing return none. 92 00:05:57,930 --> 00:06:01,800 That's why we get none here. 93 00:06:02,880 --> 00:06:08,180 So in other words, grits will be equal to none to that object. 94 00:06:08,190 --> 00:06:09,300 And that's why. 95 00:06:10,040 --> 00:06:11,000 When it prints. 96 00:06:11,000 --> 00:06:19,070 Here we are printing the non object, the object that the function greets returns. 97 00:06:19,310 --> 00:06:22,100 So you don't want to confuse print with return. 98 00:06:24,850 --> 00:06:28,750 Always try to return the output instead of printing it out. 99 00:06:31,180 --> 00:06:36,070 So if I run the script now, we get the correct expected output. 100 00:06:36,100 --> 00:06:40,910 Hey, hey, print it out by this and hello by that. 101 00:06:40,930 --> 00:06:45,190 So why is it important to return and not print? 102 00:06:45,460 --> 00:06:49,720 Well, because perhaps you want to do something to that. 103 00:06:50,830 --> 00:06:52,340 Value, which is Hello. 104 00:06:52,360 --> 00:06:55,620 Perhaps you want to print out the length of Hello. 105 00:06:55,630 --> 00:07:02,050 So the length would be Len greeting you run this and you get five. 106 00:07:02,560 --> 00:07:04,690 But if you had print here. 107 00:07:08,640 --> 00:07:09,870 See what we get now. 108 00:07:10,500 --> 00:07:18,330 It's an error because you're trying to apply Len to non to the non type object, and that gives an error 109 00:07:18,330 --> 00:07:24,600 because the non object doesn't have a length, doesn't have characters like a string has or at least 110 00:07:24,630 --> 00:07:25,440 has. 111 00:07:27,020 --> 00:07:33,740 So again, I cannot stress it enough that you should return instead of printing. 112 00:07:35,480 --> 00:07:40,340 So this was about functions for this code experiments for today. 113 00:07:40,520 --> 00:07:41,210 Thanks a lot. 114 00:07:41,240 --> 00:07:41,660 See you.