1 00:00:05,340 --> 00:00:08,890 So in the previous video, we started talking about the for loop in Python. 2 00:00:08,890 --> 00:00:12,370 So let's actually continue on with that now with a few more advanced examples. 3 00:00:12,370 --> 00:00:15,760 So I'm gonna actually delete the code that we had from the previous video. 4 00:00:15,760 --> 00:00:21,020 And just a bit of a recap, that unlike many other languages such as C and C++, 5 00:00:21,020 --> 00:00:26,390 for loops in Python work by having a variable iterate over a set of values. 6 00:00:26,390 --> 00:00:31,590 So the difference is with C and C++ and Java, for loops can be read as something 7 00:00:31,590 --> 00:00:37,750 along the lines of for i starting at 1 up to 20 in steps of 1, do something. 8 00:00:37,750 --> 00:00:40,350 If Python, the follow-ups read more like, for 9 00:00:40,350 --> 00:00:43,680 i, taking each of the values in the following sequence, do something. 10 00:00:43,680 --> 00:00:46,360 Now it doesn't sound like there's a great difference with that. 11 00:00:46,360 --> 00:00:51,320 But the actual difference of the different approach to for loops that Python uses, 12 00:00:51,320 --> 00:00:54,940 makes it really powerful, incredibly powerful, but also very flexible. 13 00:00:54,940 --> 00:00:59,050 So in our example in previous video, we wanted to show a follow with an index 14 00:00:59,050 --> 00:01:01,960 taking values from zero to the length of the string. 15 00:01:01,960 --> 00:01:05,970 But because the string is a sequence, what we can actually do is we can simplify that 16 00:01:05,970 --> 00:01:10,420 a great deal and set our loop variable to each of the characters in the sequence. 17 00:01:10,420 --> 00:01:12,520 So it sort of cuts out a step there, if you will. 18 00:01:12,520 --> 00:01:16,050 Now what we could do is we could leave the variable name as i, but we'll change it to 19 00:01:16,050 --> 00:01:19,630 char because it's no longer being used as an index in the string. 20 00:01:19,630 --> 00:01:21,610 And this will actually work better, make more sense, 21 00:01:21,610 --> 00:01:23,320 if you see the code up there on top. 22 00:01:23,320 --> 00:01:27,020 So in this example it's also a string of length one rather than integers sideways. 23 00:01:27,020 --> 00:01:28,680 So let's just have a look at that code now. 24 00:01:28,680 --> 00:01:29,890 So I'm going to type that number again. 25 00:01:29,890 --> 00:01:34,940 So what I'll do is undo that and go just to the first line, the first two lines, 26 00:01:34,940 --> 00:01:36,930 we'll keep those because we need to clean one as well. 27 00:01:36,930 --> 00:01:40,050 I'll just delete this and redo it again so it make sense as I'm typing it. 28 00:01:40,050 --> 00:01:46,110 So this time instead of using the len and so forth, you know the len for the number. 29 00:01:46,110 --> 00:01:50,980 We can put for char in number. 30 00:01:50,980 --> 00:01:55,760 And what that's going to do is extract a character that each position in that 31 00:01:55,760 --> 00:01:57,060 number string. 32 00:01:57,060 --> 00:02:05,660 And then we can put something like if char in 0123456789 colon. 33 00:02:05,660 --> 00:02:07,790 If it is, then we do the same as we did before. 34 00:02:07,790 --> 00:02:13,400 CleanedNumber, equals, cleanedNumber plus char. 35 00:02:13,400 --> 00:02:17,240 So, again, we're not having to use that number and the index position with the i 36 00:02:17,240 --> 00:02:20,760 anymore because we're actually using the for char directly. 37 00:02:20,760 --> 00:02:24,060 And, again, getting back to the for loop, your number. 38 00:02:25,690 --> 00:02:32,800 As it was before enter cleanedNumber, print the number. 39 00:02:32,800 --> 00:02:36,930 Is the format number. 40 00:02:36,930 --> 00:02:39,940 We should find this works exactly the same as it did before. 41 00:02:39,940 --> 00:02:41,510 Number is 92, blah, blah, blah, blah, blah, 87. 42 00:02:41,510 --> 00:02:47,380 But, you notice how this has significantly reduced the amount of code for and number. 43 00:02:47,380 --> 00:02:49,560 And it's actually a lot more readable as well. 44 00:02:49,560 --> 00:02:51,650 We no have to use that i number anymore. 45 00:02:51,650 --> 00:02:55,050 And we no longer have to access each of the characters by using number and 46 00:02:55,050 --> 00:02:57,040 i in square brackets as we used previously. 47 00:02:57,040 --> 00:02:58,270 So, just to confirm that the for 48 00:02:58,270 --> 00:03:02,260 loop assigns each character in the sequence number to a loop 49 00:03:02,260 --> 00:03:06,720 variable character as it's going through each element in the actual string itself. 50 00:03:06,720 --> 00:03:10,060 So each time around the loop the variable char has the value of the next character 51 00:03:10,060 --> 00:03:10,960 from our string number. 52 00:03:10,960 --> 00:03:13,880 Now, we're gonna be actually looking at lists soon, but 53 00:03:13,880 --> 00:03:17,010 a list is just a sequence of things that we can use a for 54 00:03:17,010 --> 00:03:20,750 loop for to iterate through them, as in this examples. 55 00:03:20,750 --> 00:03:22,820 I'm actually talk some more code to show you what I mean. 56 00:03:22,820 --> 00:03:29,760 So, I'm gonna put something like for, 57 00:03:29,760 --> 00:03:34,460 state in ["not pinin", 58 00:03:34,460 --> 00:03:41,420 "no more"] a stiff, bereft of life. 59 00:03:41,420 --> 00:03:44,120 We'll run this and then we will just go through and talk about it. 60 00:03:45,390 --> 00:03:47,690 This parrot is plus state and 61 00:03:47,690 --> 00:03:51,660 that's opposed to doing something like this, print. 62 00:03:51,660 --> 00:03:57,350 This parrot is, you could have done, 63 00:03:57,350 --> 00:04:00,040 .format state. 64 00:04:00,040 --> 00:04:02,650 Now not because our sequence was a list of strings, you can see here. 65 00:04:02,650 --> 00:04:04,360 We've actually got a list of strings. 66 00:04:04,360 --> 00:04:09,270 So that's actually square bracket and the list of strings separated with commas. 67 00:04:09,270 --> 00:04:11,140 Now, because of that, because it's a sequence of strings, 68 00:04:11,140 --> 00:04:15,510 we can just state to the text this parrot is plus state. 69 00:04:15,510 --> 00:04:18,079 And what it's gonna do each time it goes through the loop, 70 00:04:18,079 --> 00:04:20,790 it's going to actually add one of these to it automatically. 71 00:04:20,790 --> 00:04:22,460 And best way to see this is actually run it. 72 00:04:23,570 --> 00:04:27,430 This parrot is, you see the first time it went through, not that one there. 73 00:04:27,430 --> 00:04:30,790 The second time I went through the for loop, is no more. 74 00:04:30,790 --> 00:04:35,260 This parrot, is a stiff, and fourth this parrot is bereft of life, 75 00:04:35,260 --> 00:04:36,840 that's supposed to be, not lift. 76 00:04:36,840 --> 00:04:37,700 [LAUGH] Of life. 77 00:04:37,700 --> 00:04:41,230 So you can see how the for loop is actually worked there, it's actually 78 00:04:41,230 --> 00:04:45,230 sort of went through the sequence one element at a time, so to speak. 79 00:04:45,230 --> 00:04:48,450 And just as a confirmation I've commented it out but 80 00:04:48,450 --> 00:04:52,780 we could equally put the parrot is and use ".format(state). 81 00:04:52,780 --> 00:04:56,250 And it would be up to you to decide which one you think would be more readable. 82 00:04:56,250 --> 00:04:59,520 My personal opinion is this one is more readable and is basically less 83 00:04:59,520 --> 00:05:03,120 code as well, and just you to actually look at the previous one and that is, 84 00:05:03,120 --> 00:05:08,130 okay the four state values set to each time we go through the four loop. 85 00:05:08,130 --> 00:05:13,130 And speaking of for loops the range, and we used the range previously for 86 00:05:13,130 --> 00:05:15,650 a for loop, the range is also a sequence tie. 87 00:05:15,650 --> 00:05:19,540 It just specifies the start and end, rather than listing all values. 88 00:05:19,540 --> 00:05:23,690 In other words it's like a sequence of values, much like this, but 89 00:05:23,690 --> 00:05:25,390 instead of actually listing each and all of them, 90 00:05:25,390 --> 00:05:28,610 we're actually listing just the start and the end as I mentioned. 91 00:05:28,610 --> 00:05:31,240 In actual fact, the range is more than a start and end value, but 92 00:05:31,240 --> 00:05:32,660 it can also include step. 93 00:05:32,660 --> 00:05:34,190 We haven't seen that before. 94 00:05:34,190 --> 00:05:36,430 So let's actually go through and type that in. 95 00:05:36,430 --> 00:05:41,950 So we can do something like 4 i in range 0, 100, 96 00:05:41,950 --> 00:05:46,960 but we can also introduce the third parameter which is the step. 97 00:05:46,960 --> 00:05:49,770 And that's how much it's going to jump in between each loop. 98 00:05:49,770 --> 00:05:51,280 So if we actually run this. 99 00:05:51,280 --> 00:05:53,940 Probably would be the easiest way to see 100 00:05:53,940 --> 00:05:58,760 remain.format i, so, we actually run that now. 101 00:05:58,760 --> 00:06:02,060 So, you can see it's actually started on 102 00:06:02,060 --> 00:06:05,260 element zero which would expect because we started on the value of zero. 103 00:06:05,260 --> 00:06:08,780 But, notice how it skipped to five, and that's what this third thing here, 104 00:06:08,780 --> 00:06:09,720 this step value is. 105 00:06:09,720 --> 00:06:11,750 It means to step ahead. 106 00:06:11,750 --> 00:06:14,230 How many each time we go through the loop should we had two Is. 107 00:06:14,230 --> 00:06:17,700 So, in other words, i zero, the first time five, the second time 10, 108 00:06:17,700 --> 00:06:21,220 the third time 15 and so on through until we got to 95. 109 00:06:21,220 --> 00:06:25,550 Bring them on then it goes one less than the actual range, 110 00:06:25,550 --> 00:06:27,360 the ending range that we've added here. 111 00:06:27,360 --> 00:06:31,590 And because we're stepping in values of five, I finished at 95 instead of 100. 112 00:06:31,590 --> 00:06:35,400 Now just as you've seen nesting in for [INAUDIBLE] used, if statement and so 113 00:06:35,400 --> 00:06:36,970 forth to nest model ifs. 114 00:06:36,970 --> 00:06:38,770 We can actually nest loops as well. 115 00:06:38,770 --> 00:06:41,350 So we can actually nest a for loop within another loop, 116 00:06:41,350 --> 00:06:44,110 and that's a really powerful way to process data. 117 00:06:44,110 --> 00:06:47,380 So here's an example of how we can generate the times table used to teach 118 00:06:47,380 --> 00:06:49,030 children multiplication. 119 00:06:49,030 --> 00:06:51,490 So we can put for i. 120 00:06:51,490 --> 00:06:53,470 Don't forget, making sure we're starting to the left, 121 00:06:53,470 --> 00:06:56,360 so we're not getting caught up in any previous code. 122 00:06:56,360 --> 00:06:59,180 For i in range. 123 00:06:59,180 --> 00:07:05,180 Should be i range 1,13, and obviously that's gonna go and 124 00:07:05,180 --> 00:07:09,500 give us, go through 1 and 12, 1 to 12. 125 00:07:09,500 --> 00:07:16,130 And for j in range 1 to 13 as well. 126 00:07:17,240 --> 00:07:19,090 And then we can do print. 127 00:07:19,090 --> 00:07:25,640 Times zero is two .format, and 128 00:07:25,640 --> 00:07:31,700 it's gonna be i j, i times j. 129 00:07:32,720 --> 00:07:33,730 And then we can go print. 130 00:07:33,730 --> 00:07:36,150 We can actually put a spacer 131 00:07:36,150 --> 00:07:39,690 between each major number that we're actually going through and processing. 132 00:07:39,690 --> 00:07:43,060 So if I actually run that, you can see what it's actually done there. 133 00:07:43,060 --> 00:07:44,040 Scrolling back up to the top. 134 00:07:44,040 --> 00:07:46,860 We start on the one times table, one times one is one. 135 00:07:46,860 --> 00:07:47,810 Two times one is two. 136 00:07:47,810 --> 00:07:49,280 And so on right to 12. 137 00:07:49,280 --> 00:07:52,450 Then we start at the two times table and three times table, and 138 00:07:52,450 --> 00:07:55,290 right through until we got to the last part which was a 12 times table. 139 00:07:55,290 --> 00:07:57,320 12 times 12 is 144. 140 00:07:57,320 --> 00:08:01,680 And you can see how that was created with only a minimal amount of code, and 141 00:08:01,680 --> 00:08:06,530 that also the indent level again is really important here because if we put print in 142 00:08:06,530 --> 00:08:11,210 the wrong spot, actually print it up in there to that level instead. 143 00:08:11,210 --> 00:08:13,010 We get a completely different result. 144 00:08:13,010 --> 00:08:17,490 We actually get the equal signs with each time we've actually done a calculation. 145 00:08:17,490 --> 00:08:20,770 So, again, make sure you do watch your indent levels to make sure they're 146 00:08:20,770 --> 00:08:23,610 actually in the right spot when you're actually processing your code. 147 00:08:23,610 --> 00:08:26,170 And just another thing we can do here just before we end the video. 148 00:08:26,170 --> 00:08:29,820 We can actually change the print function's n character for a tab. 149 00:08:29,820 --> 00:08:32,370 And once we do that we can actually produce a pretty neat table. 150 00:08:32,370 --> 00:08:37,880 So, we can come back up here to print and put end equals slash t and 151 00:08:37,880 --> 00:08:41,470 put a comma there as well to make it valid. 152 00:08:41,470 --> 00:08:44,200 And now you can actually run that you can see we have something completely 153 00:08:44,200 --> 00:08:46,590 different, and we're actually going from left to right now. 154 00:08:46,590 --> 00:08:49,370 And we just make this a little bit wider it will probably make more sense. 155 00:08:51,140 --> 00:08:53,130 And that would just be a way to actually expand it out. 156 00:08:53,130 --> 00:08:55,830 And actually I've got the equals sign probably shouldn't be there now with 157 00:08:55,830 --> 00:08:56,380 this example. 158 00:08:56,380 --> 00:08:58,190 So I'm just gonna comment those out. 159 00:08:58,190 --> 00:09:00,460 We run this again. 160 00:09:00,460 --> 00:09:01,950 And we're going from left to right now. 161 00:09:01,950 --> 00:09:04,970 You can see 1 times 1 is 1, 2 times 1 is 2. 162 00:09:04,970 --> 00:09:06,670 We're going right across from left right. 163 00:09:06,670 --> 00:09:08,190 And just to pretty it up a little bit more, 164 00:09:08,190 --> 00:09:12,650 what we could also do then is here on this indent level. 165 00:09:12,650 --> 00:09:13,400 Let's actually print. 166 00:09:13,400 --> 00:09:15,390 Let's go to a new line at this point, just so 167 00:09:15,390 --> 00:09:19,100 it actually reads a little bit nicer for each time we change the number. 168 00:09:19,100 --> 00:09:20,940 We'll just print an empty string like so. 169 00:09:20,940 --> 00:09:25,030 So now if we run that, you see we're going to for each times table now, and 170 00:09:25,030 --> 00:09:26,130 it's looking a little bit more order. 171 00:09:26,130 --> 00:09:27,380 So it's just another way to actually try and 172 00:09:27,380 --> 00:09:30,200 sort things from left to right, just close it. 173 00:09:30,200 --> 00:09:32,910 Run down, window down, so and again, we have to print an empty string 174 00:09:32,910 --> 00:09:37,900 after the inner loop terminates in order to start each new set of on a new line. 175 00:09:37,900 --> 00:09:40,190 And notice we didn't have to specify a character for end. 176 00:09:40,190 --> 00:09:41,380 It goes back to being a new line. 177 00:09:41,380 --> 00:09:44,390 The change to a tab is not remembered from one print call to another. 178 00:09:44,390 --> 00:09:48,630 So, in other words, doing this here is not remembered when we get to this stage. 179 00:09:48,630 --> 00:09:49,820 That doesn't override that. 180 00:09:49,820 --> 00:09:52,860 Sort of, each time you use your print statement it doesn't remember anything 181 00:09:52,860 --> 00:09:54,180 from the previous one. 182 00:09:54,180 --> 00:09:55,570 Okay, so that's actually it. 183 00:09:55,570 --> 00:09:57,590 So we're going to end this video here now. 184 00:09:57,590 --> 00:09:59,970 We're not going to actually do a challenge for the for loop. 185 00:09:59,970 --> 00:10:03,280 But believe me you'll get plenty of time to actually complete some challenges. 186 00:10:03,280 --> 00:10:05,890 So in the next video we're going to actually start talking about the continue 187 00:10:05,890 --> 00:10:08,740 and break commands which actually work hand in hand with what 188 00:10:08,740 --> 00:10:11,570 you've been learning in this section of the course. 189 00:10:11,570 --> 00:10:12,830 So I'll see you in the next video.