WEBVTT 00:00.700 --> 00:04.310 Hello and welcome back in the session about for loops of follow ups. 00:04.360 --> 00:09.440 One of the most important and most heavily used concepts and programming. 00:09.610 --> 00:15.100 And before we learned about lists and lists that contain us of many other objects so like a backpack 00:15.440 --> 00:21.580 that you put in things like a sandwich or a bottle of water or an extra T-shirt before you go hiking. 00:21.580 --> 00:28.240 And now let's assume that it's raining in your backpack and all elements get wet and what do I typically 00:28.240 --> 00:31.510 do you unpack each element and take an action on it. 00:31.510 --> 00:37.910 So in this case you are trying each element in the Sun and others call it an elemental ICE operation. 00:37.960 --> 00:44.500 But earlier we learned that however element vice operations are not a stand out behavior of lists. 00:44.560 --> 00:46.720 So let's create a list with four elements. 00:46.720 --> 00:48.020 One two three four. 00:48.040 --> 00:54.610 And now our attention is to multiply each element by two or so an element y's operation but you already 00:54.610 --> 01:01.630 know if you just put added times to we get a multiple of the list that set off so actually we created 01:01.660 --> 01:07.720 two copies of L and then we concatenated it but we didn't get an element y's operation. 01:07.780 --> 01:13.930 But now what should we do if we want to f an element y's operation and they are the far keyword comes 01:13.930 --> 01:14.580 into place. 01:14.620 --> 01:20.830 So we are saying for j in lists that we can also say for element in lists 01:25.150 --> 01:29.020 we can name the each element of the list with the name we want. 01:29.020 --> 01:35.890 We can say element or i or j and that's important so we can say for element for each element and list 01:35.920 --> 01:37.780 and then we have to make a colon. 01:38.320 --> 01:43.330 And if you print that and if you press return then we automatically pass and make serial indent and 01:43.330 --> 01:51.950 then we say print the element so we can see here we iterated over all elements and we printed all elements 01:51.960 --> 01:53.700 so we get one two three four. 01:53.740 --> 01:59.380 And of course we can do more than just printing we can say okay each element we want to multiply by 01:59.380 --> 02:01.240 two and then print it. 02:01.270 --> 02:02.290 We can also do that 02:05.450 --> 02:12.770 and also we can say that we name each element either Multiply each side by two and then rename the multiplied 02:12.800 --> 02:17.400 element as J and then print Chase so we get the same result of course. 02:17.540 --> 02:24.260 And before we learned the function length so with the function length we can determine the amount of 02:24.260 --> 02:30.230 elements and unless we can replicate this process by a few lines of code so we can say count equals 02:30.230 --> 02:35.810 zero and four element or four under slash in list please increase my count 02:38.450 --> 02:39.500 sum count as far. 02:39.500 --> 02:44.190 So we just determined the length of our list L four elements. 02:44.530 --> 02:48.020 Again I one wanted to highlight two things so you need the colon here. 02:48.050 --> 02:56.500 So it's the same with an if statement if you forget the colon you get an error message and we need to. 02:56.520 --> 02:57.270 The intent here. 02:57.270 --> 03:00.230 So if you forget the intent we also gotten our message 03:03.580 --> 03:05.570 though this is still the right structure. 03:05.580 --> 03:12.810 So before I said we can iterate over all its rebels Soviet era appearance objects that contain many 03:12.900 --> 03:16.580 elements and also we learned that a string also is a contain of many elements. 03:16.580 --> 03:21.930 So for example the string dock contains three characters d o a.. 03:22.110 --> 03:29.640 And they let us create the rival D equal stock and then we can also iterate over D and print all single 03:29.640 --> 03:32.690 element D O T. 03:33.090 --> 03:39.360 And we can also print each character as an upper character so we can say for each character in D please 03:39.360 --> 03:47.370 print me in the upper character and we get D O T and we can also determine the length of our string 03:47.670 --> 03:49.110 and of course it's three 03:51.930 --> 03:57.180 at this point I want to introduce the range object and arrange object is also an interval so we can 03:57.180 --> 04:05.730 iterate over all elements and in this example the range object stops integers from 1 including until 04:05.910 --> 04:15.360 5 excluding So if you're under so you only get here the range object from 1 to 5 and we can also check 04:15.360 --> 04:21.720 the tape of the range object its range object and when I say the range object stops then the elements 04:21.720 --> 04:28.020 it's the action of really storing it it just makes itself ready to give me all elements if I explicitly 04:28.410 --> 04:33.900 want to have them so I can explicitly call the range object by creating a list 04:37.100 --> 04:42.870 and then the list is containing all four elements of our range object we can also iterate over arrange 04:42.900 --> 04:51.420 objects or same with the list so we can say for Aeon range 1 to 5 please print me all elements and we 04:51.420 --> 04:52.730 get 1 2 3 4. 04:52.740 --> 05:00.120 So the last element excluding So from 1 including 2 5 excluding and this is actually the same behavior 05:00.150 --> 05:03.990 as the list so before we had our list. 05:04.020 --> 05:10.590 1 2 3 4 and we iterated over it and we got all the elements. 05:10.590 --> 05:12.420 So what's the difference to our list. 05:12.420 --> 05:17.750 Well a list once created it stops all elements of the list at the same time. 05:17.760 --> 05:24.510 And of course we can iterate over all elements but the range object arrange object never stops all elements 05:24.630 --> 05:30.610 of it at the same time so we can iterate element wise of all elements of the Range object and Python 05:30.630 --> 05:37.990 internally stores only the actual element so we iterate over one element to something that this element. 05:38.130 --> 05:44.400 Now after we finish and want to go through the next element then Python drops out our actual element 05:44.430 --> 05:50.550 and takes it out of memory and then takes the next elements or Python never stops more than one element 05:50.550 --> 05:54.640 at the same time with the Range object and that's quite memory efficient. 05:54.690 --> 06:00.720 So if you assume we don't have an element or Range object with four elements but with one million elements 06:00.720 --> 06:05.710 so it makes a difference if we store million elements like only one one element. 06:05.730 --> 06:06.150 All right. 06:06.150 --> 06:12.580 So let's go on with the Range object and of course we can create 5 iterations so we can say 40 in range. 06:12.600 --> 06:16.070 5 and 5 stands for the last element. 06:16.140 --> 06:21.300 So excluding by default our starting element is 0. 06:21.300 --> 06:28.410 So here we get all elements from 1 to 4 and we can also do it explicitly we can say we want the Range 06:28.410 --> 06:36.090 object from 0 including 2 10 excluding but only every third element so we can also define this one here 06:37.350 --> 06:40.560 and then we get 0 0 3 6 and 9. 06:40.660 --> 06:47.220 Of course we can do more than just printing we can for example multiply each element in our range object 06:47.220 --> 06:56.640 and print it out and then we get all multiplied elements from 1 to 10 including let's go to our very 06:56.700 --> 06:57.840 common workflow. 06:57.840 --> 07:05.440 So we want to store the crowd numbers from 1 to 10 in our list and therefore we create an empty list. 07:05.460 --> 07:13.500 L We iterate over the Range object the from 1 to 10 including we calculate the square number for each 07:13.500 --> 07:20.820 element and call its career and then we append each scrap number to the list ever so let's see what 07:20.820 --> 07:21.620 we get here. 07:23.850 --> 07:29.240 So we get an list with ask that numbers from 1 to 10 and that's also quite a concept. 07:29.270 --> 07:33.230 Call it the list comprehension which does actually the same top. 07:33.300 --> 07:37.300 So we can say here we create here. 07:37.440 --> 07:39.890 And the spare brackets that we create a list here. 07:39.900 --> 07:47.370 We can say please for all elements in our range Object 1 till 10 please give us the element to the power 07:47.370 --> 07:54.570 of 2 and please start in a list and it's a case execute the sale and they can see if we get the same 07:54.570 --> 07:55.530 result as before. 07:55.530 --> 08:03.130 So we reduced three lines or four lines of code to only one line of code with the list comprehension. 08:03.150 --> 08:10.020 All right so let's go on with the number case study and let's count on numbers between 0 and ten thousand 08:10.440 --> 08:14.610 that are divisible by 2 and 5 without remainder. 08:14.610 --> 08:23.560 So we can say for Aeon range ten thousand one so we want to include ten thousand and if one model or 08:23.550 --> 08:25.770 two is zero. 08:25.860 --> 08:33.930 So if one is divisible by 2 without remainder and one model of 5 equals zero then increase our count 08:33.930 --> 08:34.450 by 1. 08:34.450 --> 08:40.530 So first here at the beginning we introduce the account equal equals zero and end for each element in 08:40.530 --> 08:49.050 our range object that fulfills both conditions we have an end statement please increase our count and 08:49.050 --> 08:56.340 then we get 1001 elements that fulfill the conditions so obviously a zero for first our condition and 08:56.340 --> 09:03.730 then 10 20 30 and ten thousand so each elements that are actually divisible by 10. 09:03.780 --> 09:08.550 All right so that's for the time being and the next session we will have a look at the key arguments 09:08.550 --> 09:10.980 are key words continue break and pass. 09:10.980 --> 09:12.380 So see you there by.