1 00:00:04,860 --> 00:00:08,610 Now that we've seen what a function is, and how to write them, let's practice writing 2 00:01:42,360 --> 00:01:46,060 Alright, so I'm going to call the new function is_palindrome, 3 00:01:46,060 --> 00:01:49,160 and we're going to add it after our multiply function, 4 00:01:49,160 --> 00:01:54,120 down here. Now remember to leave two blank lines after multiply. Functions 5 00:01:54,120 --> 00:01:58,530 are separated from each other with two blank lines. I'm going to start typing on 6 00:01:58,530 --> 00:02:03,650 line six; def is_palindrome 7 00:02:03,920 --> 00:02:12,220 parentheses string and then a colon outside the parentheses, and press ENTER there. 8 00:02:12,220 --> 00:02:16,320 IntelliJ has automatically indented the next line, because it knows 9 00:02:16,320 --> 00:02:20,760 that we're about to type a new block of code. Note that we've now got an error in 10 00:02:20,760 --> 00:02:24,080 the main part of the code, on line eight. That's normal. 11 00:02:24,080 --> 00:02:28,380 A function definition must be followed by an indented block of code, and we 12 00:02:28,380 --> 00:02:32,540 haven't written that yet. IntelliJ is telling us that an indent is expected, 13 00:02:32,540 --> 00:02:37,060 and that can be confusing when you first start writing functions. Don't worry though, 14 00:02:37,060 --> 00:02:41,280 the error will be fixed as soon as we enter the body of our function 15 00:02:41,280 --> 00:02:45,420 Okay, so to check if a word is a palindrome, we can just reverse it and 16 00:02:45,420 --> 00:02:49,890 check if it's equal to the original word. So I'm going to shorten this code in a 17 00:02:49,890 --> 00:02:54,000 moment. For now I'll write it in a slightly longer way, to make it clearer 18 00:02:54,000 --> 00:03:02,200 what we're doing. So on line seven I'm going to type backwards is equal to string 19 00:03:02,200 --> 00:03:08,160 square brackets, and in the square brackets, colon colon minus one, and on 20 00:03:08,160 --> 00:03:18,300 the next line, I'm going to type return backwards equal equals, or equal to string. 21 00:03:18,300 --> 00:03:19,600 Then I'm going to leave two black lines 22 00:03:19,610 --> 00:03:24,140 after the end of our function as well. So hopefully, the code that I've added should 23 00:03:24,140 --> 00:03:29,600 be easy to understand. The slice on line seven reverses the original string. 24 00:03:29,600 --> 00:03:34,680 On line eight, we check if the reverse string is the same as the original. If it is, 25 00:03:34,680 --> 00:03:41,000 we return True, otherwise, we return False. The expression backwards equals 26 00:03:41,000 --> 00:03:45,200 equal string will evaluate to either True or False, and that's the result that 27 00:03:45,200 --> 00:03:49,160 the function will return. In fact, we could do all that with one line of code. 28 00:03:49,160 --> 00:03:51,710 You'll often find this written in a more concise way, 29 00:03:51,710 --> 00:03:55,610 so let's comment out lines seven and eight. Instead what I'm going to do on 30 00:03:55,610 --> 00:04:02,990 line nine, is type return string square brackets, and within the square brackets, 31 00:04:02,990 --> 00:04:08,360 colon colon minus one again, and outside the square brackets, equals 32 00:04:08,360 --> 00:04:16,120 equals string, and making sure there's two blank lines at the end of our function. 33 00:04:16,120 --> 00:04:19,920 So that's more concise and more like real code, but when you're learning, 34 00:04:19,920 --> 00:04:23,560 don't worry about splitting lines up into several parts - it's more important 35 00:04:23,560 --> 00:04:28,880 to write code that you understand, rather than writing the shortest code possible. 36 00:04:28,880 --> 00:04:33,380 If you find lines seven and eight easier to understand than line nine at this stage, 37 00:04:33,380 --> 00:04:37,340 then that's fine. Your code will naturally get more concise, as you get 38 00:04:37,340 --> 00:04:41,630 more comfortable and more experienced in programming. Alright, so let's see if 39 00:04:41,630 --> 00:04:47,640 this works. I'm going to delete all the code from line twelve and onwards. 40 00:04:47,640 --> 00:04:51,240 Now that I've done that we need to write some code to test this new function. 41 00:04:51,240 --> 00:04:58,760 On line 12 I'm going to type word equals input parentheses double quotes, 42 00:04:58,760 --> 00:05:06,000 Please enter a word to check. We'll add a colon and a space there as well. 43 00:05:06,000 --> 00:05:12,260 Next line, we're going to do a test; if is_palindrome parentheses and 44 00:05:12,260 --> 00:05:18,220 pass word as an argument, and a colon. The next line we're going to do a print 45 00:05:18,220 --> 00:05:22,280 parentheses double quotes. Then I'm going to add a single quote and 46 00:05:22,280 --> 00:05:26,390 add our replacement fields, left and right curly braces and another single quote, 47 00:05:26,390 --> 00:05:32,960 is a palindrome double quote dot format word, 48 00:05:32,960 --> 00:05:38,180 and the two right parentheses. And on line 15 I'm going to type else : Then we need to 49 00:05:38,180 --> 00:05:42,590 print a message for where it's not a palindrome, so print parentheses double 50 00:05:42,590 --> 00:05:47,240 quotes single quote, our replacement fields, left right curly braces, single 51 00:05:47,240 --> 00:05:55,220 quote is not a palindrome. We want a double quote again, dot format and 52 00:05:55,220 --> 00:05:59,640 word in parentheses, and close off the line like so 53 00:05:59,640 --> 00:06:03,400 Alright, so now that we've done that, let's run the program 54 00:06:03,400 --> 00:06:08,200 and see if it works. So I'm going to click into the run window and I'm going to 55 00:06:08,200 --> 00:06:15,310 enter racecar, racecar, racecar is a palindrome, and our function's returning 56 00:06:15,310 --> 00:06:18,729 True, which is what we want to see. So test the program with a few more words to 57 00:06:18,729 --> 00:06:22,530 be confident that it works. Just to be sure 58 00:06:22,530 --> 00:06:29,300 I'll enter a word that isn't a palindrome, Python, Python is not a palindrome. 59 00:06:29,300 --> 00:06:33,560 It seems to be working, well sort of. What happens if I enter radar 60 00:06:33,560 --> 00:06:37,920 with a capital R. Let's try that and see what happens. 61 00:06:39,220 --> 00:06:43,940 That's not good. Palindromes shouldn't consider the case of the letters. 62 00:06:43,940 --> 00:06:48,560 We had better fix that, which sounds like a good challenge. 63 00:07:06,380 --> 00:07:09,860 So that's the challenge - see how you go with it. I'll go over my solution to it 64 00:07:09,860 --> 00:07:12,660 in the next video.