WEBVTT 1 00:00:00.040 --> 00:00:02.520 Welcome back to the deep dive. Today. We're getting into 2 00:00:02.560 --> 00:00:05.839 the foundations, specifically Python three programming. 3 00:00:06.080 --> 00:00:09.240 That's right, and we're basing this on some really solid 4 00:00:09.359 --> 00:00:13.359 material excerpts from a Beginner's Guide, part of the Undergraduate 5 00:00:13.400 --> 00:00:17.280 Topics and Computer Science series, peer reviewed expert. 6 00:00:16.839 --> 00:00:19.839 Author right, and the book itself is aimed at people 7 00:00:20.239 --> 00:00:24.519 starting from scratch, maybe zero programming knowledge, but wants to 8 00:00:24.559 --> 00:00:28.879 get them up to speed as capable Python developers exactly. 9 00:00:29.199 --> 00:00:31.160 So our goal here is to kind of pull out 10 00:00:31.160 --> 00:00:35.479 the key takeaways, give you that shortcut to the core 11 00:00:35.560 --> 00:00:36.759 ideas of Python. 12 00:00:36.439 --> 00:00:38.759 Three, distilled version from a trusted source. 13 00:00:38.560 --> 00:00:41.200 Precisely getting the best bits without reading the whole thing 14 00:00:41.240 --> 00:00:41.799 cover to cover. 15 00:00:42.039 --> 00:00:45.479 Okay, let's jump right in Python itself. Is it fundamentally 16 00:00:45.520 --> 00:00:47.640 and maybe what's a key thing that sets it apart 17 00:00:47.719 --> 00:00:48.200 early on? 18 00:00:48.679 --> 00:00:51.439 Sure? Well, at its heart it's a general purpose language. 19 00:00:51.439 --> 00:00:54.439 You hear it alongside CE plus plus T, JavaScript, Java, 20 00:00:54.520 --> 00:00:58.039 that kind of thing, and a really defining characteristic the 21 00:00:58.079 --> 00:01:00.960 book flags immediately is dynamic typing. 22 00:01:01.119 --> 00:01:03.960 Dynamic typing, okay, so that means a variable isn't locked 23 00:01:03.960 --> 00:01:05.359 into one data type. 24 00:01:05.400 --> 00:01:08.799 Exactly, that you can have a variable holding say a number, 25 00:01:09.200 --> 00:01:11.599 and then later on you can assign text a string 26 00:01:12.000 --> 00:01:13.560 to that same variable name. 27 00:01:13.799 --> 00:01:17.359 Python's fine with it, uh huh, unlike say Java or 28 00:01:17.400 --> 00:01:19.680 c sharp, where you declare the type up front and 29 00:01:19.719 --> 00:01:20.359 it's fixed. 30 00:01:20.640 --> 00:01:23.079 Right. That adds a lot of flexibility, which is a 31 00:01:23.120 --> 00:01:24.319 big part of Python's appeal. 32 00:01:24.519 --> 00:01:30.400 Interesting and the name Python it's not about snakes, h No. 33 00:01:30.319 --> 00:01:32.799 Not directly. It was created back in the eighties by 34 00:01:32.879 --> 00:01:35.879 Guido van Rossum in the Netherlands. Yeah, and he named 35 00:01:35.920 --> 00:01:38.840 it after Monty Python's flying Circus big fan. 36 00:01:39.200 --> 00:01:40.799 Seriously, that's brilliant. 37 00:01:40.879 --> 00:01:43.359 Yeah, and the book mentions you'll even find little nods 38 00:01:43.359 --> 00:01:46.719 to the show in Python's official documentation sometimes. 39 00:01:46.840 --> 00:01:48.879 Love that bit of personality definitely. 40 00:01:49.239 --> 00:01:51.560 And yeah, just to confirm we are laser focused on 41 00:01:51.640 --> 00:01:53.359 Python three here as that's what the. 42 00:01:53.280 --> 00:01:57.200 Source covers got it now. The book brings up programming paradigms, 43 00:01:57.239 --> 00:01:59.439 different ways to structure code. It starts with. 44 00:02:00.560 --> 00:02:03.599 Right, Procedural programming is sort of the classic approach. Think 45 00:02:03.640 --> 00:02:07.000 of it like a recipe, a sequence of explicit instructions. 46 00:02:07.439 --> 00:02:10.599 You break the steps down into procedures or functions and 47 00:02:10.759 --> 00:02:14.120 use things like if statements and loops to control the flow. 48 00:02:14.280 --> 00:02:15.960 Like see your Pascal exactly. 49 00:02:16.039 --> 00:02:18.599 Those are prime examples. It's a good starting point to 50 00:02:18.680 --> 00:02:21.360 understand how programs can be organized before we maybe get 51 00:02:21.360 --> 00:02:24.680 into other styles later like functional or object oriented. 52 00:02:24.800 --> 00:02:28.479 Makes sense, but okay, before writing any code, you need 53 00:02:28.520 --> 00:02:31.080 the tools. Setting up the environment. 54 00:02:30.759 --> 00:02:34.479 Yep, fundamental step. The book recommends the most direct route 55 00:02:34.759 --> 00:02:37.639 go to the official Python website Python dot org. Python 56 00:02:37.680 --> 00:02:40.439 dot org, I find the downloads link, grab the installer 57 00:02:40.479 --> 00:02:43.639 for your system, Windows, Mac, Linux, They're all. 58 00:02:43.479 --> 00:02:46.080 There, and part of installing is making sure your computer 59 00:02:46.120 --> 00:02:48.759 can find Python right. The path variable thing. 60 00:02:48.759 --> 00:02:52.080 Crucial point, especially on Windows. You need Python on your 61 00:02:52.120 --> 00:02:54.599 system's path, so you can just open a terminal or 62 00:02:54.639 --> 00:02:57.120 command prompt type Python and it works. 63 00:02:56.960 --> 00:02:59.240 Right, so it's accessible from anywhere exactly. 64 00:02:59.639 --> 00:03:02.840 The book also really pushes using a good code editor 65 00:03:03.240 --> 00:03:08.039 or even better, an ID an integrated development environment. 66 00:03:07.719 --> 00:03:10.039 So something more than just basic notepad. 67 00:03:10.360 --> 00:03:14.120 Definitely. It mentions Sublime text as a good text editor 68 00:03:14.159 --> 00:03:17.759 to start with. It understands Python syntax does color coding 69 00:03:17.960 --> 00:03:20.840 makes things much easier to read, okay, but for more 70 00:03:20.879 --> 00:03:25.800 involved projects. It flags a full ID as being really beneficial. 71 00:03:25.479 --> 00:03:27.680 And the recommendation there is pie Charm PI. 72 00:03:27.680 --> 00:03:31.120 Charm from Jet Brains. Yeah, it's described as a full workbench. 73 00:03:31.400 --> 00:03:35.719 It has code completion, debugging tools, integrated version control like get, 74 00:03:36.039 --> 00:03:38.560 lots of features that become really helpful as you progress. 75 00:03:38.680 --> 00:03:41.719 Jet Brain's website for that one, and the example code 76 00:03:41.719 --> 00:03:42.680 from the book itself. 77 00:03:42.759 --> 00:03:45.400 Two main ways suggested. If you've got GET installed, you 78 00:03:45.400 --> 00:03:47.800 can just use get clone with the GitHub link provided 79 00:03:47.800 --> 00:03:49.360 in the book, or if you don't have get, then 80 00:03:49.400 --> 00:03:50.960 you can usually just download the whole thing as a 81 00:03:51.039 --> 00:03:54.159 ZIP file directly from that same GitHub page. And as 82 00:03:54.199 --> 00:03:56.599 the book knows, IDEs like pie Charm often have Get 83 00:03:56.599 --> 00:03:58.919 built in any way, which makes cloning easier. 84 00:03:59.000 --> 00:04:04.360 Okay, environments now the traditional first program Hello World, the classic. 85 00:04:04.520 --> 00:04:07.039 It's really just a sanity check, you know, does the 86 00:04:07.039 --> 00:04:10.639 interpreter run? Does my editor save the file correctly? Are 87 00:04:10.680 --> 00:04:11.479 the settings okay? 88 00:04:11.560 --> 00:04:14.479 And Python files usually have the dot pi extension correct. 89 00:04:14.560 --> 00:04:17.240 Dot PI is the standard and the key piece of 90 00:04:17.279 --> 00:04:21.040 code for Hello World is the print function that's. 91 00:04:20.839 --> 00:04:22.800 Built in part of Python itself. 92 00:04:22.920 --> 00:04:26.600 Yep, a fundamental built in function. It's how you tell 93 00:04:26.639 --> 00:04:29.000 your program to display output on the screen. 94 00:04:29.439 --> 00:04:32.639 Then the book makes it interactive pretty quickly with input. 95 00:04:32.519 --> 00:04:36.160 Right flips the script dot input. Let's the program ask you, 96 00:04:36.360 --> 00:04:38.879 the user, a question, it shows a prompt. 97 00:04:38.560 --> 00:04:40.160 Message whatever text you give it. 98 00:04:40.120 --> 00:04:42.319 Exactly, then a weads for you to type something and 99 00:04:42.399 --> 00:04:45.839 press enter. Whatever you typed comes back into the program 100 00:04:46.040 --> 00:04:47.720 as a string as text. 101 00:04:47.480 --> 00:04:50.199 Data, which means you need somewhere to store that input 102 00:04:50.720 --> 00:04:52.000 enter variables. 103 00:04:51.720 --> 00:04:55.120 Perfect lead in variables are essentially named storage spots in 104 00:04:55.160 --> 00:04:57.839 the computer's memory. You give a piece of data a name, 105 00:04:58.040 --> 00:04:59.480 a label so you can refer to it. 106 00:04:59.519 --> 00:05:02.720 Later username in the example exactly. 107 00:05:02.519 --> 00:05:06.319 And dining back to dynamic typing, that username variable holds 108 00:05:06.360 --> 00:05:09.079 the string from the input function, but you could theoretically 109 00:05:09.120 --> 00:05:11.439 assign a number to username later if you want it. 110 00:05:11.639 --> 00:05:16.480 So the sequence print Hello World, then username input under 111 00:05:16.519 --> 00:05:19.000 your name using the equals sign. 112 00:05:19.199 --> 00:05:21.879 The assignment operator right assigns the result of the input 113 00:05:21.959 --> 00:05:24.480 function to the variable username, and. 114 00:05:24.439 --> 00:05:28.839 Then print hello username. That shows print can handle multiple things. 115 00:05:28.920 --> 00:05:32.680 Yeah, you can give print multiple arguments separated by commas, 116 00:05:33.079 --> 00:05:36.439 like the literal text hello and the value stored in 117 00:05:36.480 --> 00:05:39.199 the username variable. It prints them out, usually with a 118 00:05:39.240 --> 00:05:42.480 space in between by default. A neat little demonstration. 119 00:05:42.040 --> 00:05:45.839 Simple but covers input, output, variables, assignment. Nice. 120 00:05:46.000 --> 00:05:47.600 It's those core building blocks. 121 00:05:47.360 --> 00:05:49.439 Okay, let's talk more about those building blocks, the basic 122 00:05:49.519 --> 00:05:50.079 data types. 123 00:05:50.160 --> 00:05:53.920 The source focuses on four key ones to start strings, 124 00:05:54.160 --> 00:05:58.759 text numbers, integers and floating point Boollian's true false, and 125 00:05:58.800 --> 00:05:59.959 this special value none. 126 00:06:00.160 --> 00:06:02.639 Strings first, text inside quotes yep. 127 00:06:02.959 --> 00:06:06.199 Single quotes like this or double quotes like this functionally 128 00:06:06.240 --> 00:06:09.480 identical in Python. The book mentioned single quotes are maybe 129 00:06:09.560 --> 00:06:12.879 slightly more common sort of the Pythonic convention, but both 130 00:06:12.920 --> 00:06:13.480 work fine. 131 00:06:13.720 --> 00:06:17.639 And strings aren't just static texts. They have operations methods. 132 00:06:17.920 --> 00:06:20.279 Oh yeah, lots of useful built in methods, things like 133 00:06:20.519 --> 00:06:23.000 split to break a string into a list of words, 134 00:06:23.000 --> 00:06:25.040 starts with or ends with to check. 135 00:06:24.920 --> 00:06:27.120 The beginning or end case checking two dot I supper 136 00:06:27.199 --> 00:06:28.360 eyes lower. 137 00:06:28.319 --> 00:06:31.079 Or dot isselfa to see if it's all letters. Very 138 00:06:31.120 --> 00:06:34.040 handy stuff, and case matters in comparisons. 139 00:06:34.120 --> 00:06:36.560 So Python is different from Python absolutely. 140 00:06:36.920 --> 00:06:39.800 If you want to compare strings regardless of case, the 141 00:06:39.920 --> 00:06:42.560 usual trick is to convert both to lower case first 142 00:06:43.000 --> 00:06:48.079 using dot lower so misstring dot lower Hello. Method names 143 00:06:48.120 --> 00:06:49.639 are also case sensitive, naturally. 144 00:06:49.800 --> 00:06:52.600 The book also mentions a way to format strings using 145 00:06:52.680 --> 00:06:53.759 string dot template. 146 00:06:54.000 --> 00:06:57.000 Yeah, that's one method. You create a template with placeholders 147 00:06:57.199 --> 00:06:59.920 like two hood and then use the dot substitute method 148 00:07:00.040 --> 00:07:03.360 to fill in those placeholders with actual values. There's also 149 00:07:03.439 --> 00:07:06.360 dot save substitute, which is useful because it won't raise 150 00:07:06.360 --> 00:07:08.120 an error if you forget to provide a value for 151 00:07:08.160 --> 00:07:10.519 a placeholder, It just leaves the placeholder texts. 152 00:07:10.639 --> 00:07:13.920 As is, moving on to numbers, integers and floats. 153 00:07:14.079 --> 00:07:17.360 Integers are whole numbers like ten naked five zero zero. 154 00:07:17.759 --> 00:07:20.160 Floats are numbers with a decimal point like three point 155 00:07:20.160 --> 00:07:23.319 one four next zero point five. Python uses a standard 156 00:07:23.319 --> 00:07:26.079 format called i EEE seven five to four for. 157 00:07:26.079 --> 00:07:28.160 Floats, and you can convert between them. 158 00:07:28.079 --> 00:07:31.759 Yes, using the end and float functions in three point 159 00:07:31.839 --> 00:07:34.279 nine O three boards. It truncates, just chops off the 160 00:07:34.319 --> 00:07:37.160 decimal part, doesn't round. Float five gives five point. 161 00:07:37.000 --> 00:07:40.160 Zero arithmetic a standard plus heat division. 162 00:07:40.199 --> 00:07:44.199 Okay, division's interesting. The single slash always results in a slot. 163 00:07:44.319 --> 00:07:46.040 Even four to two gives two point zero always a 164 00:07:46.040 --> 00:07:49.439 float always if you specifically want integer division the whole 165 00:07:49.519 --> 00:07:52.319 number result, throwing away any remainder you use the double 166 00:07:52.360 --> 00:07:54.279 slash move. So five two is two got it. 167 00:07:54.560 --> 00:07:56.560 For float division? For integer division, and. 168 00:07:56.519 --> 00:07:59.000 If you mix types like adding an integer in a float, 169 00:07:59.040 --> 00:08:01.720 the result will always be promoted to a float makes sense. 170 00:08:01.959 --> 00:08:03.399 Boolean's next true and. 171 00:08:03.360 --> 00:08:07.079 False the bedrock of decision making capital T capital F. 172 00:08:08.079 --> 00:08:10.879 The book points out a slightly quirky detail. Technically, there 173 00:08:10.920 --> 00:08:14.040 are subtype of integers really and true is one and 174 00:08:14.240 --> 00:08:17.600 false as zero, and conversely boole one is true, zero, 175 00:08:18.160 --> 00:08:21.879 zero is false. Non zero numbers are generally true, zero. 176 00:08:21.680 --> 00:08:25.079 Is false interesting connection, and the last one. None. 177 00:08:25.240 --> 00:08:28.160 None is Python's special way to signify the absence of 178 00:08:28.160 --> 00:08:30.360 a value. It's not zero, it's not an empty straying, 179 00:08:30.480 --> 00:08:34.320 it's just nothing. It has its own unique type none type. 180 00:08:34.440 --> 00:08:35.320 When would you use it? 181 00:08:35.559 --> 00:08:38.399 Often is a default value, or maybe a function returns 182 00:08:39.360 --> 00:08:41.679 none if it couldn't compute a result for some reason. 183 00:08:41.440 --> 00:08:43.799 And checking for it. The book says, use is none. 184 00:08:43.639 --> 00:08:46.440 Yes, variable is none, or variable is not none. That's 185 00:08:46.480 --> 00:08:49.399 the preferred, most reliable way to check if something holds 186 00:08:49.440 --> 00:08:53.360 the none value. Using none can sometimes work, but is 187 00:08:53.399 --> 00:08:54.799 safer and more idiomatic. 188 00:08:54.879 --> 00:08:58.200 Okay, data typees covered now. Making the program do things 189 00:08:58.240 --> 00:09:02.039 based on conditions or repeat actions control flow if statements first. 190 00:09:02.039 --> 00:09:06.200 Right, the fundamental decision maker if condition. If that condition 191 00:09:06.240 --> 00:09:10.039 evaluates too true, the indented block of code underneath it runs. 192 00:09:10.279 --> 00:09:14.159 If not it's skipped, and that indentation is crucial absolutely 193 00:09:14.200 --> 00:09:15.279 non negotiable in Python. 194 00:09:15.399 --> 00:09:18.600 Unlike languages that use curly braces, Python uses white space 195 00:09:19.000 --> 00:09:22.679 the indentation level to define which lines of code belong 196 00:09:22.759 --> 00:09:25.480 to the If block or else or loops or functions 197 00:09:26.080 --> 00:09:28.399 get it wrong, you get errors or incorrect logic. 198 00:09:28.480 --> 00:09:30.279 The standard is four spaces four. 199 00:09:30.159 --> 00:09:32.559 Spaces per indentation level is the strong convention. 200 00:09:32.679 --> 00:09:36.440 Yeah, okay, So if block runs code if true, what 201 00:09:36.600 --> 00:09:37.399 if it's fault? 202 00:09:37.480 --> 00:09:39.559 That's where else comes in ye if condition total one 203 00:09:39.600 --> 00:09:41.799 block runs if true, the other runs if. 204 00:09:41.679 --> 00:09:44.279 False, and for more than two options you use. 205 00:09:44.279 --> 00:09:46.840 Lf sure for else. If if condition one, l if 206 00:09:47.120 --> 00:09:50.120 condition two, l's condition three, I guess. Python checks each 207 00:09:50.120 --> 00:09:52.840 condition in order. The first one that's true gets executed, 208 00:09:53.000 --> 00:09:55.200 and the rest, including the final else, are skipped. 209 00:09:55.360 --> 00:09:58.519 Can you put if statements inside other if statements? 210 00:09:58.600 --> 00:10:01.399 Sure? That's called nesting really valid, though deep nesting can 211 00:10:01.440 --> 00:10:04.399 sometimes make code harder to read. The book also briefly 212 00:10:04.440 --> 00:10:05.720 mentions if expressions. 213 00:10:06.000 --> 00:10:06.679 What are those? 214 00:10:07.080 --> 00:10:11.279 It's like a compressed ifels that produces a value often 215 00:10:11.360 --> 00:10:14.639 used directly in assignments like result is value a true 216 00:10:14.679 --> 00:10:18.240 if condition else value a false it's a neat shorthand 217 00:10:18.240 --> 00:10:19.080 for simple cases. 218 00:10:19.440 --> 00:10:23.159 Okay, decisions covered. What about repetition loops. 219 00:10:22.919 --> 00:10:27.039 Two main kinds while and four. A while loop keeps 220 00:10:27.080 --> 00:10:31.240 executing its block of code as long as its condition remains. 221 00:10:30.919 --> 00:10:32.919 True, so you need to make sure that the condition 222 00:10:33.000 --> 00:10:34.639 eventually becomes false exactly. 223 00:10:34.639 --> 00:10:37.279 Otherwise you have an infinite loop, and you usually need 224 00:10:37.320 --> 00:10:39.879 to set up the variable used in the condition before 225 00:10:39.919 --> 00:10:42.879 the loop starts. And loops four loops are generally used 226 00:10:42.879 --> 00:10:45.440 when you want to iterate over a sequence of items, 227 00:10:45.480 --> 00:10:47.720 like all the elements in a list, where characters in 228 00:10:47.759 --> 00:10:50.000 a string or specific range of numbers. 229 00:10:50.120 --> 00:10:52.320 Often clearer when you know how many times you need 230 00:10:52.360 --> 00:10:53.120 to loop. 231 00:10:53.000 --> 00:10:55.399 Yeah, or when you're processing each item in a collection. 232 00:10:55.879 --> 00:10:58.759 The structure for item and collection is very common and 233 00:10:58.799 --> 00:10:59.679 readable in Python. 234 00:11:00.120 --> 00:11:03.240 What if your looping, say, searching for something, and you 235 00:11:03.320 --> 00:11:05.399 find it early, can you stop the loop? 236 00:11:05.559 --> 00:11:08.159 Yes, that's what the brake statement is for. It immediately 237 00:11:08.240 --> 00:11:10.919 exits the current innermost while or for loop. 238 00:11:10.960 --> 00:11:14.679 You're in okay, and the book mentions a weird four 239 00:11:14.759 --> 00:11:15.679 else construct. 240 00:11:15.919 --> 00:11:18.960 Ah, yes, the loop else. It's a bit unusual if 241 00:11:18.960 --> 00:11:22.279 you're coming from other languages. An else block attached to 242 00:11:22.320 --> 00:11:25.720 a for loop or while executes only if the loop 243 00:11:25.759 --> 00:11:29.159 completed normally, meaning it went through all its iterations without 244 00:11:29.279 --> 00:11:30.559 encountering a break statement. 245 00:11:30.639 --> 00:11:33.360 So if you break out the else's skipt correct. 246 00:11:33.399 --> 00:11:35.720 It's often used in search loops. If the loop finishes 247 00:11:35.759 --> 00:11:38.840 and the elf block runs, it means the break never happened. 248 00:11:38.879 --> 00:11:40.399 Therefore the item wasn't found. 249 00:11:40.720 --> 00:11:45.039 Huh, that's actually quite clever. Okay. As programs grow, just 250 00:11:45.080 --> 00:11:48.559 having one long sequence of code isn't practical. Functions are 251 00:11:48.600 --> 00:11:49.039 the answer. 252 00:11:49.200 --> 00:11:52.360 Absolutely essential. Functions let you package up a piece of code, 253 00:11:52.480 --> 00:11:54.840 give it a name, and reuse it. They're key to 254 00:11:54.879 --> 00:11:59.759 breaking down large, complex problems into smaller, more manageable, testable units. 255 00:12:00.039 --> 00:12:03.320 BOK connects this to something called functional decomposition. 256 00:12:02.840 --> 00:12:05.600 Right, that's a more formal term from software analysis. It's 257 00:12:05.639 --> 00:12:08.639 the process of identifying the main tasks your system needs 258 00:12:08.639 --> 00:12:12.519 to perform, representing them as functions, and then breaking down 259 00:12:12.559 --> 00:12:16.759 those functions into smaller subfunctions, focusing on inputs, outputs, and 260 00:12:16.799 --> 00:12:18.080 the transformation. 261 00:12:17.559 --> 00:12:21.519 Process and it mentions. Flow charts and data dictionaries alongside. 262 00:12:21.080 --> 00:12:24.879 This, Yeah, as related tools. Flow charts help visualize this 263 00:12:24.960 --> 00:12:28.159 sequence of steps and decisions in an algorithm. While data 264 00:12:28.159 --> 00:12:31.399 dictionaries provide a central place to define and describe all 265 00:12:31.440 --> 00:12:35.480 the data elements your system uses, useful for planning and documentation. 266 00:12:35.960 --> 00:12:38.200 So defining a function in Python starts with. 267 00:12:38.320 --> 00:12:42.320 Death deaf function name, parameters, followed by the colon and 268 00:12:42.399 --> 00:12:45.679 the indented block of code that makes up the function's body. Again, 269 00:12:45.720 --> 00:12:48.559 that four S based enden convention is standard, and the 270 00:12:48.639 --> 00:12:52.480 doc string oh very important for documentation. It's a string 271 00:12:52.759 --> 00:12:55.240 literal place right at the beginning of the function body 272 00:12:55.320 --> 00:12:58.480 inside cripple quotes. Usually it explains what the function does, 273 00:12:58.559 --> 00:13:00.639 what its parameters are, what a return, urns, et cetera. 274 00:13:01.000 --> 00:13:04.720 It's not just a comment. Tools can automatically extract this information. 275 00:13:05.039 --> 00:13:07.919 Parameters are in the definition. Arguments are what you pass 276 00:13:07.960 --> 00:13:08.559 when you call it. 277 00:13:08.879 --> 00:13:13.240 Correct parameters are the names used inside the function. Arguments 278 00:13:13.279 --> 00:13:16.039 are the actual value supplied when the function is called. 279 00:13:17.120 --> 00:13:20.279 The book then gets into some powerful argument handling features 280 00:13:21.320 --> 00:13:22.919 ARGs and quarks. 281 00:13:23.120 --> 00:13:25.279 Right for when you don't know how many arguments will be. 282 00:13:25.279 --> 00:13:30.360 Passed Exactlygs inside the function definition collects any extra positional 283 00:13:30.480 --> 00:13:34.159 arguments one's passed just by position into a a tupo okay, 284 00:13:34.360 --> 00:13:37.320 and quary's collects any extra keyword arguments one's past is 285 00:13:37.399 --> 00:13:40.519 name value into a dictionary. You can use them together. 286 00:13:41.080 --> 00:13:44.080 The book highlights this as really useful for library authors 287 00:13:44.120 --> 00:13:46.279 who want to offer flexibility to their users. 288 00:13:46.399 --> 00:13:48.000 And Lambda functions. 289 00:13:47.759 --> 00:13:51.679 Lambdas are for creating small, anonymous functions in line. If 290 00:13:51.679 --> 00:13:53.919 you need a simple function just for one quick use, 291 00:13:54.200 --> 00:13:56.799 maybe as an argument to another function, lambda lets you 292 00:13:56.799 --> 00:13:58.960 define it right there without a full deaf statement. 293 00:13:59.279 --> 00:14:01.960 The book suggest us using the number guessing game as 294 00:14:01.960 --> 00:14:04.440 an exercise for function refactoring. 295 00:14:04.679 --> 00:14:07.159 Yeah, taking a simple script and breaking its logic down 296 00:14:07.200 --> 00:14:09.600 into well defined functions is a great way to practice this. 297 00:14:09.679 --> 00:14:13.600 Structuring functions also introduce the idea of variable scope, where 298 00:14:13.639 --> 00:14:14.639 a variable. 299 00:14:14.240 --> 00:14:18.480 Lives crucial concept. Variables defined right at the top level 300 00:14:18.480 --> 00:14:22.799 of a script outside any function have global scope. They 301 00:14:22.840 --> 00:14:25.840 can in principle be accessed from anywhere. 302 00:14:25.960 --> 00:14:28.000 The variables inside a function. 303 00:14:28.080 --> 00:14:31.399 They have local scope. They only exist and are accessible 304 00:14:31.519 --> 00:14:34.679 within that function. If you have a local variable with 305 00:14:34.720 --> 00:14:37.480 the same name as a global variable, the local one 306 00:14:37.519 --> 00:14:40.559 takes precedence inside the function. They are distinct. 307 00:14:40.879 --> 00:14:43.039 What if you need to change a global variable from 308 00:14:43.120 --> 00:14:44.200 inside a function. 309 00:14:44.240 --> 00:14:46.960 You have to explicitly tell Python that's your intention using 310 00:14:47.000 --> 00:14:50.240 the global keyword global, we will bovar at the start 311 00:14:50.279 --> 00:14:52.279 of the function says when I use my global of 312 00:14:52.399 --> 00:14:54.080 ar here, I mean the global one, not a new 313 00:14:54.120 --> 00:14:54.600 local one. 314 00:14:54.639 --> 00:14:57.159 Okay, and non local. That's where nested functions. 315 00:14:57.440 --> 00:15:00.399 Right. If you define a function inside another one function, 316 00:15:00.759 --> 00:15:03.399 nesting non local is used in the inner function to 317 00:15:03.480 --> 00:15:07.159 refer to a variable in the directly enclosing function scope, 318 00:15:07.600 --> 00:15:10.320 but not the global scope. The example in the book 319 00:15:10.360 --> 00:15:13.200 shows an interfunction modifying a variable belonging to the outer 320 00:15:13.279 --> 00:15:14.600 function using non local. 321 00:15:14.759 --> 00:15:20.159 That clarifies the difference. Now a potentially tricky concept recursion. 322 00:15:19.960 --> 00:15:23.679 Ah recursion a function calling itself. It's a way to 323 00:15:23.720 --> 00:15:27.480 solve problems by breaking them down into smaller, self similar 324 00:15:27.519 --> 00:15:28.279 sub problems. 325 00:15:28.320 --> 00:15:30.440 The key is having an escape patch right. A base 326 00:15:30.480 --> 00:15:31.759 case absolutely essential. 327 00:15:31.960 --> 00:15:35.519 The base case or termination condition is the simplest version 328 00:15:35.559 --> 00:15:38.159 of the problem that the function can solve directly without 329 00:15:38.159 --> 00:15:41.840 calling itself again. This stops the chain of calls. Without it, 330 00:15:41.879 --> 00:15:44.480 you get infinite recursion and eventually a recursion er. 331 00:15:44.679 --> 00:15:46.759 Factorial is the textbook example. 332 00:15:46.840 --> 00:15:51.559 It is factorial n is n factorial n one until 333 00:15:51.600 --> 00:15:53.720 you hit the base case factorial one, which is just 334 00:15:53.799 --> 00:15:56.120 one the book traces how the calls stack up and 335 00:15:56.159 --> 00:15:58.360 then unwind to produce the final result. 336 00:15:58.480 --> 00:16:01.519 How does it stack up against just using a loop iteration? 337 00:16:01.799 --> 00:16:04.840 Recursion can often lead to a very elegant, concise code 338 00:16:04.879 --> 00:16:08.960 that mirrors the mathematical definition of a problem. However, iteration 339 00:16:09.320 --> 00:16:12.120 using loops is generally more efficient in terms of speed 340 00:16:12.159 --> 00:16:15.720 and memory usage in Python and many other languages. The 341 00:16:15.759 --> 00:16:18.720 book does mention that some languages, particularly functional ones, can 342 00:16:18.759 --> 00:16:22.120 optimize tail recursion into iteration, removing the overhead. 343 00:16:22.279 --> 00:16:25.639 Speaking of functional, let's shift to that programming style. How 344 00:16:25.639 --> 00:16:28.840 does the book contrast it with procedural. 345 00:16:28.759 --> 00:16:31.559 It's presented as a different mindset. The core idea in 346 00:16:31.559 --> 00:16:35.360 functional programming is to think about computation more like evaluating 347 00:16:35.360 --> 00:16:39.360 mathematical functions. A key principle is avoiding side effects. 348 00:16:39.480 --> 00:16:41.679 Side effects meaning changes to. 349 00:16:41.639 --> 00:16:45.799 State outside the function itself. A pure functions output depends 350 00:16:45.840 --> 00:16:49.039 only on its input arguments and it doesn't modify anything 351 00:16:49.080 --> 00:16:52.799 external like a global variable or a file. This makes 352 00:16:52.879 --> 00:16:55.879 code easier to reason about and test because you know 353 00:16:56.000 --> 00:16:59.240 exactly what it does based on its inputs alone. This 354 00:16:59.279 --> 00:17:01.840 relates to ref prential transparency. 355 00:17:01.200 --> 00:17:03.279 Which means you can replace the function call with its 356 00:17:03.320 --> 00:17:04.519 result pretty much. 357 00:17:04.880 --> 00:17:07.279 If a function is pure, substituting its call with its 358 00:17:07.319 --> 00:17:11.000 return value for the same inputs won't change the program's 359 00:17:11.039 --> 00:17:14.319 overall behavior. Big win for predictability. 360 00:17:13.759 --> 00:17:15.440 And immutable data is encouraged. 361 00:17:15.799 --> 00:17:20.359 Yes, using data structures that cannot be changed after creation. 362 00:17:20.960 --> 00:17:23.559 Python strings are a good example. When you seem to 363 00:17:23.559 --> 00:17:26.799 modify a string, you're actually creating a new string object. 364 00:17:27.759 --> 00:17:31.839 Working with immutable data helps prevent accidental side effects. Because 365 00:17:31.880 --> 00:17:34.759 functions can't secretly change data that other parts of the 366 00:17:34.759 --> 00:17:37.519 program rely on, they return new data. 367 00:17:37.279 --> 00:17:39.960 Instead, and recursion fits naturally here. 368 00:17:40.079 --> 00:17:44.000 Functional programming often emphasizes recursion as a primary control structure, 369 00:17:44.240 --> 00:17:47.079 fitting the mathematical function model well, though as we said, 370 00:17:47.119 --> 00:17:50.279 iteration is still possible and often more performant in practice 371 00:17:50.319 --> 00:17:50.799 in Python. 372 00:17:51.119 --> 00:17:54.240 What advantages does this style offer, according to. 373 00:17:54.240 --> 00:17:57.000 The book, potential for less code, code that's easier to 374 00:17:57.079 --> 00:18:01.599 understand and test due to purity, easier parallelization since pure 375 00:18:01.599 --> 00:18:04.880 functions don't interfere with each other, and sometimes very elegant 376 00:18:05.000 --> 00:18:06.039 retursive solutions. 377 00:18:06.079 --> 00:18:07.759 Any downsides mentioned. 378 00:18:07.480 --> 00:18:11.920 Things like handling continuous input output or interactive systems can 379 00:18:11.960 --> 00:18:16.400 feel less natural with a purely functional approach. Historically, there 380 00:18:16.440 --> 00:18:20.000 were performance concerns, though that's less true now, and the 381 00:18:20.039 --> 00:18:23.480 style the idioms might feel less intuitive at first if 382 00:18:23.480 --> 00:18:27.279 you're used to procedural or ooprogramming, sometimes perceived as a 383 00:18:27.359 --> 00:18:30.960 bit academic, though functional features are increasingly mainstream. 384 00:18:31.319 --> 00:18:34.440 Got it. This leads into higher order functions. What makes 385 00:18:34.440 --> 00:18:36.240 a function higher order. 386 00:18:36.319 --> 00:18:38.519 It comes from the fact that functions in Python are 387 00:18:38.559 --> 00:18:42.079 first class objects. You can assign them to variables, store 388 00:18:42.119 --> 00:18:45.480 them in data structures, pass them as arguments to other functions, 389 00:18:45.640 --> 00:18:47.640 and return them from functions, just. 390 00:18:47.640 --> 00:18:50.039 Like any other data type like a number or a string. 391 00:18:50.240 --> 00:18:53.160 Exactly. A higher order function is simply a function that 392 00:18:53.240 --> 00:18:57.039 either takes one or more functions as arguments or returns 393 00:18:57.039 --> 00:18:59.160 a function as its result, or both. 394 00:18:59.319 --> 00:19:01.799 Key consop functional programming, very much so. 395 00:19:02.119 --> 00:19:05.200 The book shows examples like passing a calculation function into 396 00:19:05.240 --> 00:19:08.720 another function to tax salary tax funk, or a function 397 00:19:08.759 --> 00:19:11.240 that takes an action function applied data. 398 00:19:11.039 --> 00:19:15.079 Action funk, and functions returning functions that leads to closures. 399 00:19:15.720 --> 00:19:19.200 Yes, when a function defined inside another function an inner 400 00:19:19.240 --> 00:19:22.319 function is returned, it carries with it the environment of 401 00:19:22.400 --> 00:19:26.000