WEBVTT 00:02.200 --> 00:04.440 Hello everybody and welcome back to the costs. 00:04.440 --> 00:09.200 So in the last session we learned how to check whether that condition is true or false. 00:09.220 --> 00:16.690 And paisan returned as a true or false but so-called boolean objects so typically checking whether their 00:16.690 --> 00:23.260 condition is true or false is only 50 percent of our job because in real world situations we first have 00:23.260 --> 00:29.970 to check whether a condition is true and if so we have to take action one and a false. 00:29.980 --> 00:31.300 We have to take action too. 00:31.300 --> 00:39.820 So here's the point where we introduce if elif and s statements that are doing a very good job here 00:39.820 --> 00:42.070 in Python. 00:42.160 --> 00:46.440 So first of all we define two variables A and B equals five. 00:46.690 --> 00:50.220 And then we check whether A is less than 10. 00:50.220 --> 00:52.590 So we start with the keyword. 00:52.600 --> 01:02.870 If if a less than 10 and then we need a colon and then we press enter and you can see it here. 01:02.890 --> 01:05.340 Python makes automatically and indent. 01:05.560 --> 01:08.770 And now we have to define what our accent is here. 01:08.770 --> 01:10.030 If our statement. 01:10.030 --> 01:10.600 Yes correct. 01:10.600 --> 01:12.700 So obviously our statement is correct. 01:12.700 --> 01:21.830 So our accent should be please print me a is less than 10. 01:22.110 --> 01:28.570 So let's check what happens if we run the cell so we get A's less than 10. 01:28.580 --> 01:29.210 That's correct. 01:29.630 --> 01:36.680 So now what happens if we change here the comparison operator to a is greater than 10. 01:36.950 --> 01:39.330 So obviously the statement is false. 01:39.440 --> 01:43.430 So let's see what happens so Python prints nothing. 01:43.440 --> 01:44.810 So the statement is not true. 01:44.820 --> 01:48.980 So we don't have to take action one which is print A is less than 10. 01:48.990 --> 01:58.740 So now we have to define an alternative action and then we introduce the keyword else you make a colon 01:58.740 --> 02:03.530 on press enter and then you can see also here Python makes automatically and. 02:04.350 --> 02:07.210 And then and then we define our alternative action. 02:07.220 --> 02:10.970 So if the statement is greater than 10 it's not true. 02:11.100 --> 02:14.550 What should be the action and the action here is print 02:17.280 --> 02:22.870 a is not greater than 10. 02:23.190 --> 02:28.690 So let's see what happens if we run the cell we get the message a is not greater than tetanus. 02:28.700 --> 02:29.440 That's correct. 02:29.450 --> 02:31.910 So now if you change again here the operator 02:35.140 --> 02:37.650 is less than 10 and we execute again. 02:37.660 --> 02:40.520 Then we get again is less than 10. 02:40.570 --> 02:46.360 So what Python makes here internally is actually checks whether the conduit condition goes through and 02:46.360 --> 02:51.970 then as it is true it takes the action print and then uh passes and stops. 02:51.990 --> 02:56.100 So there are some sources for mistakes here and statements. 02:56.140 --> 02:57.240 You need to make the colon. 02:57.270 --> 02:57.420 Yeah. 02:57.430 --> 03:01.400 If you forget the colon then we get an error message. 03:01.600 --> 03:03.100 So the colon is important. 03:03.670 --> 03:09.640 And also here the intent you have to make the indent here if you don't make it make the indent here. 03:09.700 --> 03:11.210 You get them error message. 03:13.480 --> 03:19.450 And typically paste and makes the indent automatically if you press here enter after the colon and you 03:19.450 --> 03:22.740 can also by pressing the key tab. 03:22.810 --> 03:29.200 You can make the indent here and also for the eight F statements of the US statement so you have the 03:29.200 --> 03:31.970 same and then there's then the if statement. 03:31.970 --> 03:37.230 So if the h s statement has another indent it also doesn't work. 03:37.240 --> 03:43.840 So the that men should have the same end as the f statement and the axiom here in this case the print 03:43.840 --> 03:46.150 statements should have phone and indent. 03:46.180 --> 03:47.520 So this this year. 03:47.530 --> 03:48.100 Correct. 03:48.100 --> 03:48.510 All right. 03:48.520 --> 03:51.940 So let's move to another example and we compare a and b. 03:51.940 --> 03:58.720 So if a is greater than B which is not the case then please print a is not greater than B. 03:59.530 --> 04:06.160 So if this statement is not true Python then checks if our alternative condition Elif. 04:06.190 --> 04:10.120 So that's the keyword for checking an alternative condition. 04:10.120 --> 04:18.130 So as of a is less than B but to see also not the case please print me is less than B and this is also 04:18.130 --> 04:19.120 false. 04:19.150 --> 04:22.840 So Python continues and then there's the s statement. 04:22.840 --> 04:28.960 So if condition one and condition two they're both false then in all other cases please print me a C 04:28.960 --> 04:35.500 could be a and b in this case of course Python prints a is equal to B and again but Python does internally 04:35.500 --> 04:43.000 it checks in the first condition if it's true it takes action one and stops and if a condition one is 04:43.000 --> 04:49.700 not true it checks a condition two and if condition two is true it takes the action of condition two 04:49.720 --> 04:58.420 and then stops and yeah if all statements are conditions are not true then Python does the action which 04:58.420 --> 05:03.820 is determined by the s statements or for all other cases and we see now on the next example that we 05:03.820 --> 05:06.430 can have more than one elif statement. 05:06.430 --> 05:12.760 So now let's assume that we are ordering some goods in an online web shop and we get some discounts 05:12.760 --> 05:14.460 depending on our price. 05:14.710 --> 05:16.610 And there are some discount targets. 05:16.630 --> 05:23.670 So if the price is lower than 50 dollars we get a zero percent discount if it's between 50 and 100. 05:23.710 --> 05:32.970 So 50 including until 100 excluding we get 10 percent discount if our prices in the entire were 100 05:32.980 --> 05:36.810 including to 200 excluding a 20 percent discount. 05:36.820 --> 05:43.900 And if our price is equal or greater than two hundred dollar or we get a discount of 25 percent we can 05:43.900 --> 05:49.720 transform this into a code and say so if our price is less than our discount and Turnbull at positions 05:49.720 --> 05:57.220 there also if our price is less than 50 you will get a discount of 0 percent and then Elif. 05:57.250 --> 06:04.170 So if this statement is not correct but the price is less than 100 we get a discount of 10 percent. 06:04.210 --> 06:12.090 And if also this condition is not true then we check if our price is less than 200 and also if this 06:12.090 --> 06:17.970 is not true then we know that our price must be greater than 200 or greater equal than two hundred and 06:18.120 --> 06:23.970 in all other cases here greater than two hundred our discount is 25 percent. 06:23.970 --> 06:25.020 So now let's check this. 06:25.020 --> 06:29.660 Our price is seventy five dollars and we run here. 06:29.670 --> 06:35.600 Our if and Elif statements our offer discount price is sixty seven point five. 06:35.910 --> 06:43.350 So we get 10 percent discount because our prices in the interval 50 to 100 where we get 10 percent discount. 06:43.830 --> 06:52.680 And also let's assume if we have a price of 40 so I would assume to get a zero percent discount and 06:52.680 --> 06:54.740 our after this comprises 40. 06:55.390 --> 06:57.750 And also let's assume our prices 1000 07:01.220 --> 07:04.220 we get an after discount prices of 750. 07:04.220 --> 07:06.160 So we get 25 percent discount. 07:06.770 --> 07:09.380 And we can further increase them the elif statement. 07:09.380 --> 07:11.780 So there is no restriction on the Ellis statements. 07:11.780 --> 07:15.230 We cannot fear let's say 50 Elif statements. 07:15.230 --> 07:17.210 So this is quite flexible here. 07:17.210 --> 07:19.760 All right so let's move on to the vile Lou. 07:19.850 --> 07:28.400 So let's set eight to 10 and let's check whether a is less than 20 and if it is less than 20 we increase 07:28.430 --> 07:29.850 a by 1. 07:29.870 --> 07:36.560 So this this year a plus equals one is the same as a equals a plus 1. 07:36.560 --> 07:38.650 So that's an abbreviation here. 07:38.660 --> 07:45.100 We can do that so if a is less than 20 year please increase a by one and print a and let's see what 07:45.100 --> 07:45.480 happens. 07:45.490 --> 07:52.420 A fear on the sale so we get 11 and then we can rerun again because now is eleven and we can check again 07:52.420 --> 07:53.890 if it's less than 20. 07:54.760 --> 07:59.200 Now we got 12 and we can repeat this process many times 08:02.030 --> 08:05.410 until we it reads uh 20 in the end. 08:05.900 --> 08:11.980 So that s second. 08:12.010 --> 08:17.740 So now we have reached 20 and now if you rerun the cell again we check whether a is less than 20 or 08:17.770 --> 08:21.880 so 20 is less than 20 and that is this is a false statement. 08:22.000 --> 08:24.480 And here our loop stops. 08:24.610 --> 08:24.780 Yeah. 08:24.790 --> 08:31.240 And as you can see here I mean it's a bit inconvenient to do this process or to repeat this process 08:31.240 --> 08:32.070 manually. 08:32.230 --> 08:34.850 And they are the while loop comes into play. 08:35.110 --> 08:39.950 So we actually do the same task as Sierra buff but introduce the device statement. 08:39.970 --> 08:45.960 And we define a that's 10 and then we make an hour repeated. 08:46.810 --> 08:55.420 If statement and check whether a is less than 20 and if it's the case we increase a by 1 here and print 08:55.450 --> 08:55.730 a. 08:55.940 --> 08:59.360 And so now let's see what happens. 08:59.440 --> 09:02.030 So Python automatically does um. 09:02.100 --> 09:04.410 The repetition of our if statement. 09:04.420 --> 09:07.850 So you know the first check is um a s 10. 09:07.900 --> 09:14.440 So the first step is uh Python checks whether 10 is less than 20 in this case that increases a by 1 09:14.440 --> 09:15.670 and prints a. 09:15.680 --> 09:20.280 And now Python repeats the process so it takes a equals eleven. 09:20.290 --> 09:22.420 Checks that it's less than 20. 09:22.420 --> 09:23.890 That's correct. 09:23.900 --> 09:25.000 Increases a by 1. 09:25.000 --> 09:26.510 And again prints a lot. 09:26.560 --> 09:31.280 There's twelve Python repeats the process until we reach a equals twenty. 09:31.540 --> 09:32.770 And this is all automated. 09:32.770 --> 09:35.110 So we don't have to to make this manually. 09:35.110 --> 09:37.690 And that's the purpose of a bi loop. 09:37.840 --> 09:42.250 And then in the end we can we can also print again a check. 09:42.250 --> 09:42.540 Okay. 09:42.550 --> 09:44.050 This is our final result. 09:44.440 --> 09:54.020 So the value stopped when a is 20 for let's move onto a more moralistic case here a more real world 09:54.020 --> 10:01.280 situation to say so let's assume we are in charge of loading a container ship and we have to check if 10:01.340 --> 10:08.440 the freight exceeds the maximum freight that is allowed and we assume here that the maximum allowed 10:08.440 --> 10:10.550 weight of 1000 tonnes. 10:10.580 --> 10:18.140 And our actual weight is 1100 tons and we have many containers on our ship and we can reduce our freight 10:18.140 --> 10:20.930 by unloading a container. 10:21.020 --> 10:27.760 And we assume that a container is way to 70 tonnes so past that we can reduce the weight by 17 tonnes. 10:27.830 --> 10:30.500 And so we are introducing here a while loop. 10:30.530 --> 10:37.220 So we are checking if our weight is greater than our maximum allowed weight and if this is the case 10:37.250 --> 10:43.700 we print the caution statement of freight with X tonnes is too heavy and then the next step we reduce 10:43.700 --> 10:50.870 our weight uh with the by our reduction steps so we unload one container and we will put this process 10:51.290 --> 10:57.430 so many times until our actual weight is less or is not greater than our maximum weight. 10:57.650 --> 11:02.450 And in the end we reach it and our while loop stops we print. 11:02.490 --> 11:04.190 Um the final result. 11:04.220 --> 11:06.040 The freight with X tonsils. 11:06.050 --> 11:07.220 Okay. 11:07.380 --> 11:12.230 And um yeah let's assume that our our actual weight is 1100 tonnes. 11:12.230 --> 11:17.930 So it's it's heavier than our max weight and let's check what pace does here. 11:18.110 --> 11:23.330 So it first checks as if our initial weight 1100 tonnes is okay. 11:23.330 --> 11:24.180 No it's not okay. 11:24.200 --> 11:27.650 Then it reduces our weight by 17 tonnes. 11:27.650 --> 11:31.060 And also 1000 eighty three tonnes is too heavy. 11:31.070 --> 11:36.760 And it repeats the steps so many times until we reach afraid of 998 tonnes. 11:36.770 --> 11:44.120 And here the binder stops and we get a printout that nine hundred ninety eight tonnes is okay. 11:44.480 --> 11:46.210 So this works. 11:46.210 --> 11:46.610 All right. 11:46.610 --> 11:54.230 So we learned a lot about if elif and s statements and the Y loop and the next session we are getting 11:54.230 --> 11:59.240 introduced to for loops which are also very important so see you in the next session. 11:59.270 --> 11:59.670 Thank you. 11:59.670 --> 11:59.930 Bye.