1 1 00:00:01,330 --> 00:00:02,910 Hi guys and welcome back. 2 2 00:00:02,910 --> 00:00:04,580 In this video, we're going to start learning 3 3 00:00:04,580 --> 00:00:06,320 about decorators. 4 4 00:00:06,320 --> 00:00:08,210 Decorators are great in Python 5 5 00:00:08,210 --> 00:00:12,390 because they allow us to very easily modify functions. 6 6 00:00:12,390 --> 00:00:13,940 So let's learn more about them. 7 7 00:00:15,090 --> 00:00:18,490 Here we've got a user dictionary that has a username and 8 8 00:00:18,490 --> 00:00:20,890 an access level of guest. 9 9 00:00:20,890 --> 00:00:24,167 Let's say that guests can't access this function here 10 10 00:00:24,167 --> 00:00:25,350 get_admin_password 11 11 00:00:25,350 --> 00:00:28,310 which returns the password to your admin panel. 12 12 00:00:28,310 --> 00:00:29,143 But as you can see, 13 13 00:00:29,143 --> 00:00:31,230 if we print out get_admin_password 14 14 00:00:31,230 --> 00:00:32,960 at the moment, even though we're a guest 15 15 00:00:32,960 --> 00:00:35,210 we're gonna get out 1234. 16 16 00:00:35,210 --> 00:00:36,310 There's nothing in this function 17 17 00:00:36,310 --> 00:00:37,933 to prevent us from doing that. 18 18 00:00:38,910 --> 00:00:42,360 So, the output of this video should be 19 19 00:00:43,280 --> 00:00:46,430 to get this function secured so that 20 20 00:00:46,430 --> 00:00:50,093 people that are guests cannot get the value out. 21 21 00:00:51,270 --> 00:00:54,380 Now of course, the clear thing that you can do 22 22 00:00:54,380 --> 00:00:56,320 is to put an if statement in here. 23 23 00:00:56,320 --> 00:01:01,320 If the user's access level is == to admin, 24 24 00:01:01,460 --> 00:01:03,970 then you can print out this function. 25 25 00:01:03,970 --> 00:01:05,550 Otherwise, you can't. 26 26 00:01:05,550 --> 00:01:06,424 So this will work 27 27 00:01:06,424 --> 00:01:09,140 if you run that, you don't get anything, 28 28 00:01:09,140 --> 00:01:10,360 but of course as you know, 29 29 00:01:10,360 --> 00:01:13,810 get_admin_password is still un-secure 30 30 00:01:13,810 --> 00:01:15,830 so you can still print that out 31 31 00:01:15,830 --> 00:01:17,650 and it'll still work. 32 32 00:01:17,650 --> 00:01:18,860 Because what we've done is 33 33 00:01:18,860 --> 00:01:23,860 we have protected this specific call to get_admin_password, 34 34 00:01:23,900 --> 00:01:27,290 but we haven't protected this one. 35 35 00:01:27,290 --> 00:01:30,383 So, this is probably not exactly what we want to do. 36 36 00:01:31,760 --> 00:01:32,593 The next thing we can do 37 37 00:01:32,593 --> 00:01:35,610 is we can define a secure function. 38 38 00:01:35,610 --> 00:01:37,863 For example, secure_get_admin. 39 39 00:01:38,926 --> 00:01:41,810 And in this one, if the user's access level is admin 40 40 00:01:44,240 --> 00:01:47,420 then we can return the password 1234. 41 41 00:01:47,420 --> 00:01:49,040 Now, a couple of things. 42 42 00:01:49,040 --> 00:01:51,630 Clearly get_admin_password is still defined, 43 43 00:01:51,630 --> 00:01:53,810 so that is not going to work, 44 44 00:01:53,810 --> 00:01:58,760 but secure_get_admin does protect the password. 45 45 00:01:58,760 --> 00:02:01,790 Running that gives you None, first of all 46 46 00:02:01,790 --> 00:02:03,230 when you run secure_get_admin 47 47 00:02:03,230 --> 00:02:05,350 because we didn't return 1234. 48 48 00:02:05,350 --> 00:02:07,600 Instead, we returned None which is a default. 49 49 00:02:07,600 --> 00:02:09,743 Then you get 1234 the next time around. 50 50 00:02:10,920 --> 00:02:12,580 So of course, what you may want to do 51 51 00:02:12,580 --> 00:02:14,719 is delete this one entirely. 52 52 00:02:14,719 --> 00:02:17,633 But, that poses a small problem. 53 53 00:02:17,633 --> 00:02:20,960 Which is that all the functions 54 54 00:02:20,960 --> 00:02:22,560 where you want it to be secure, 55 55 00:02:22,560 --> 00:02:25,120 you're going to have to add this if statement. 56 56 00:02:25,120 --> 00:02:27,750 And up 'til now, that is what you would have done 57 57 00:02:27,750 --> 00:02:29,760 if you didn't know about decorators. 58 58 00:02:29,760 --> 00:02:33,571 But, a decorator will allow us to modify this function 59 59 00:02:33,571 --> 00:02:36,620 to secure it without having to replace 60 60 00:02:36,620 --> 00:02:40,800 all of our functions by its secure counterparts. 61 61 00:02:40,800 --> 00:02:42,943 So, we don't want to do that either. 62 62 00:02:44,960 --> 00:02:46,050 Instead what we could do 63 63 00:02:46,050 --> 00:02:49,880 is define another function, secure_function 64 64 00:02:49,880 --> 00:02:51,170 that takes in a function. 65 65 00:02:51,170 --> 00:02:53,990 We've learned about first class functions, 66 66 00:02:53,990 --> 00:02:56,730 so we can take it in as a function there, 67 67 00:02:56,730 --> 00:03:01,590 and we'll say if the user's access level is == to admin 68 68 00:03:03,890 --> 00:03:06,040 then we will return func. 69 69 00:03:06,040 --> 00:03:07,440 Otherwise we'll return none. 70 70 00:03:07,440 --> 00:03:09,240 And now what you may be tempted to do 71 71 00:03:09,240 --> 00:03:10,470 is to do something like 72 72 00:03:10,470 --> 00:03:13,877 get_admin_password = secure function(get_admin_password). 73 73 00:03:17,850 --> 00:03:19,363 So, will this work? 74 74 00:03:20,480 --> 00:03:23,030 Well, let's run through the code. 75 75 00:03:23,030 --> 00:03:25,040 We've got secure_function being called 76 76 00:03:25,040 --> 00:03:26,970 which takes in get_admin_password, 77 77 00:03:26,970 --> 00:03:29,110 and when this line runs, 78 78 00:03:29,110 --> 00:03:31,680 we're going to check the user's access level 79 79 00:03:31,680 --> 00:03:32,860 and see if it's admin. 80 80 00:03:32,860 --> 00:03:35,793 And if it is, we're going to return func. 81 81 00:03:37,685 --> 00:03:39,035 So, let's see what happens. 82 82 00:03:41,310 --> 00:03:43,010 Now you get an error. 83 83 00:03:43,010 --> 00:03:45,560 NoneType object is not callable. 84 84 00:03:45,560 --> 00:03:48,700 Because of course, when we ran this code 85 85 00:03:48,700 --> 00:03:50,140 i.e., this line here, 86 86 00:03:50,140 --> 00:03:52,930 the user's access level was guest not admin. 87 87 00:03:52,930 --> 00:03:54,520 So we didn't return func, 88 88 00:03:54,520 --> 00:03:56,450 we returned none which is the default. 89 89 00:03:56,450 --> 00:03:59,270 So get_admin_password = none. 90 90 00:03:59,270 --> 00:04:02,320 Then we're trying to run none as if it were a function, 91 91 00:04:02,320 --> 00:04:04,520 but you can't do that so you get an error. 92 92 00:04:04,520 --> 00:04:05,580 What you would have to do is 93 93 00:04:05,580 --> 00:04:07,620 make sure that your user is an admin 94 94 00:04:07,620 --> 00:04:09,780 before you run any of your code. 95 95 00:04:09,780 --> 00:04:12,800 And then it will work and you will get 1234. 96 96 00:04:12,800 --> 00:04:16,653 So this is a step closer to what we want, 97 97 00:04:17,540 --> 00:04:21,100 but alas it requires that our user be an admin 98 98 00:04:21,100 --> 00:04:24,080 before we secure our functions. 99 99 00:04:24,080 --> 00:04:26,440 Ideally we would like to do something that checks 100 100 00:04:26,440 --> 00:04:29,480 the user's access level when you call the function, 101 101 00:04:29,480 --> 00:04:31,033 not when you define it. 102 102 00:04:32,900 --> 00:04:34,740 So, here's what we're gonna do. 103 103 00:04:34,740 --> 00:04:36,790 We're still going to take in a function 104 104 00:04:36,790 --> 00:04:40,360 but now we're going to define another function, 105 105 00:04:40,360 --> 00:04:42,270 which I'm going to call secure_function. 106 106 00:04:42,270 --> 00:04:44,603 This one I'm gonna call make_secure. 107 107 00:04:45,710 --> 00:04:48,820 This one doesn't take any parameters, 108 108 00:04:48,820 --> 00:04:50,906 and it is the one that checks. 109 109 00:04:50,906 --> 00:04:55,700 And, it returns calling the original function. 110 110 00:04:55,700 --> 00:04:59,310 Then, here we return secure_function. 111 111 00:04:59,310 --> 00:05:01,360 So this is a decorator. 112 112 00:05:01,360 --> 00:05:02,550 What happens now, and by the way 113 113 00:05:02,550 --> 00:05:04,450 this should be make_secure. 114 114 00:05:04,450 --> 00:05:06,760 What happens now is that get_admin_password, 115 115 00:05:06,760 --> 00:05:08,933 this function that we want to secure, 116 116 00:05:10,120 --> 00:05:12,810 is passed to the make_secure function. 117 117 00:05:12,810 --> 00:05:14,220 This one defines another function, 118 118 00:05:14,220 --> 00:05:16,070 and by the way, in Python you can define functions 119 119 00:05:16,070 --> 00:05:18,820 inside a function, so that's totally fine. 120 120 00:05:18,820 --> 00:05:22,050 And this function here, when called, 121 121 00:05:22,050 --> 00:05:23,940 will check the user's access level 122 122 00:05:23,940 --> 00:05:26,350 and return calling the original function 123 123 00:05:26,350 --> 00:05:27,620 which is get_admin_password. 124 124 00:05:27,620 --> 00:05:32,340 So it will return 1234 if the user's access level is admin. 125 125 00:05:32,340 --> 00:05:33,760 So that's this function here, 126 126 00:05:33,760 --> 00:05:35,680 and then we return the function itself. 127 127 00:05:35,680 --> 00:05:39,080 Not the function call, but the function itself. 128 128 00:05:39,080 --> 00:05:43,910 get_admin_password will be equal to this function. 129 129 00:05:43,910 --> 00:05:47,210 Which calls seemingly itself, but this is okay. 130 130 00:05:47,210 --> 00:05:49,423 It calls get_admin_password from up here. 131 131 00:05:50,556 --> 00:05:53,350 So when you call get_admin_password what you're gonna do 132 132 00:05:53,350 --> 00:05:55,670 is you're going to check the user's access level, 133 133 00:05:55,670 --> 00:05:58,120 and then you're going to return the result 134 134 00:05:58,120 --> 00:06:00,250 of calling the function originally, 135 135 00:06:00,250 --> 00:06:01,863 which will give you 1234. 136 136 00:06:05,709 --> 00:06:10,080 At the moment you get none, but of course if you 137 137 00:06:10,080 --> 00:06:13,290 set the user's access level to admin down here 138 138 00:06:13,290 --> 00:06:14,343 and you run it again, 139 139 00:06:15,250 --> 00:06:16,510 then you get 1234. 140 140 00:06:16,510 --> 00:06:17,860 Which is exactly what we wanted. 141 141 00:06:17,860 --> 00:06:20,800 So this is a simple decorator. 142 142 00:06:20,800 --> 00:06:23,820 This simple decorator will create a function 143 143 00:06:23,820 --> 00:06:27,730 and replace the original function with this secure one. 144 144 00:06:27,730 --> 00:06:31,870 So that you can no longer call get_admin_password 145 145 00:06:31,870 --> 00:06:34,963 without having the admin access level. 146 146 00:06:35,910 --> 00:06:38,240 Now if you wanted to add a little bit of error handling 147 147 00:06:38,240 --> 00:06:39,640 you can do an else here 148 148 00:06:39,640 --> 00:06:41,197 and you can return something like 149 149 00:06:41,197 --> 00:06:45,880 "No admin permissions for {user['username']}." 150 150 00:06:47,600 --> 00:06:50,490 and that'll give you a nicer idea of what's going on 151 151 00:06:50,490 --> 00:06:52,290 if you don't have admin permissions. 152 152 00:06:54,330 --> 00:06:55,500 That's everything for this video. 153 153 00:06:55,500 --> 00:06:57,770 This is a simple decorator, 154 154 00:06:57,770 --> 00:06:59,910 and now in the next one we're going to learn more 155 155 00:06:59,910 --> 00:07:02,700 about using the @ syntax for decorators 156 156 00:07:02,700 --> 00:07:05,520 that makes this much simpler, and much easier 157 157 00:07:05,520 --> 00:07:07,740 to re-use and secure multiple functions 158 158 00:07:07,740 --> 00:07:09,500 if that's what you want to do. 159 159 00:07:09,500 --> 00:07:10,390 Thanks for joining me, 160 160 00:07:10,390 --> 00:07:12,140 and I'll see you in the next video.