(A quick note: If you know all this already and are getting bored...CONGRATULATIONS! Here's '''[https://www.youtube.com/watch?v=x94yTpv0T1k some cute corgi puppy videos]''' as your reward. Then, come back and dive into a later section. This is all self-paced. Regardless, I recommend you do this set of lessons if you haven't programmed in Python 3 before because we build on it later and you'll be lost. If you have programmed in Python 3 before, you can just skip to the Final Exam at the end, show your stuff, and help your teammates.)
}}} We'll be starting with a programming language called [https://www.python.org/ Python], specifically Python 3. There are a lot of programming languages. Some are created because they're better for solving certain problems, others because people are bored and want to try something new. Python has been around for a while, and its pretty popular because its easy to use. The team uses Java to control the robot but that language is a little trickier. We'll get to that one later once you get a handle on the basics. Python, like every programming language, has a structure. Here are the big parts: * ''Variables'': Things you assign to and read from. Like in Algebra. `a="Dump Truck"` sets the variable A to the string "Dump Truck". You can set them to numbers to or fancy things like lists. They're basically the nouns. * ''Control Structures'': These are instructions like IF this is true THEN do that…. These are like grammar rules, like use active voice, or use punctuation. * ''Functions'': These do things. They take nouns as arguments, do something, and can return nouns. In `redCar = paintCarRed(blueCar)`, `paintCarRed` is a function. They're the verbs, they do things, and they take variables and return variables. Some functions are built in to Python, but you can create your own. * ''Packages'': A lot of other people have written functions to do things. A lot of things. When these things are bundled together they're called ''packages''. You can tell a computer to use a library and save your self a lot of typing. Much like in English, you blend all of these together to create stories, or ''programs''. Both have a beginning middle and end. So lets write the first program that all programmers start with: "Hello World" {{{ #!python a="Hello World" print(a) }}} This tells the computer to print, you guessed it, "Hello World" Now you try it...Do the following: 1. Then highlight the code above, right click and click `Copy`. This put the code on the clipboard so you can share it with another window. 1. Go [https://www.tutorialspoint.com/execute_python3_online.php here]. This site is our code editor for training purposes, and its pretty cool. You can put code in the center section, and click '''Execute''' to run it. The lower window shows the results. 1. On that page, highlight all the code already in the center window. 1. Right click and pick `Paste`. This should replace everything in the window with the contents above. 1. Finally click `Execute` right above the center window to run the program. You can see the results in the green box below (it scrolls, so look at the last lines) (From now on, we'll call this step "''Go [https://www.tutorialspoint.com/execute_python3_online.php here] and run the code above''". (Just come back to these steps if ever you forget how to do that). After a bit, you'll be rewarded with the following message in the bottom window: {{{ Hello World! }}} The program told the computer to print the value of variable a on the screen. And, boom, now you're a programmer. The rest of learning how to code is just more details. This is the end of Lesson 1. = Lesson 2: Control Structures = In lesson 1, we had you create a program, "Hello World". Now, "Hello World" is not too exciting if you want to program robots, but its an important first step. We showed you how to run a function (or verb) `print`, which does something (shows on the screen the value of its argument `a`, where `a` is assigned the value "Hello World". If you want to do more in a program and actually make decisions in your code, we need to introduce control structures. == If-Then-Else: Decide, already! == Take the program below, it uses an If-Then-Else control structure to ask the program to make a decision, and run code based on that decision. You'll use these all the time. {{{ #!python location = 'HERE' print("Welcome to our store\n") if location == 'HERE': print("We're here! Come on in\n") print("Our ours are 11:00am-11:52am\n") else: print("Go away, we're out eating tacos\n") print("Hope you had a good time") }}} ''Go [https://www.tutorialspoint.com/execute_python3_online.php here] and run the code above.'' It should print: {{{ Welcome to our store We're here! Come on in Our ours are 11:00am-11:52am Hope you had a good time }}} Three things to note about this program: 1. The double equals in `location=='HERE'` on the first line. It is called an ''expression''. In this case it is an equals expression (other kinds of comparisons in python are listed here) . It returns ''True'' when the condition evaluates to ''True'', otherwise its ''False''. Note on that line the word 'HERE' is in quotes. That's to indicate its a string (a text value) not some variable (which doesn't exist). If you used `=` instead of `==` it wouldn't work as you expected because it would be a variable assignment. If a If-Then-Else statement ever behaves in an unexpected way, check for this problem first, its a really common mistake. 1. Spacing and indents are important in Python. the line "We're here..." and the line below it are indented to indicate they are part of a statement ''block'' that runs when the condition evaluates to `True`. The second block on the else is run when the condition to `False`, and only contains one line. If you want to do stuff outside of the IF-THEN, don't indent it like the first and last print statements. 1. You'll see that a few of the print statements end with a `\n`. This is called a ''escape sequence'', and its shorthand for a newline. When the computer sees it in a print statement, it will add an extra line to the output. [[Here|https://www.quackit.com/python/reference/python_3_escape_sequences.cfm]] are some other escape sequences you can use. Now, in the editor replace the line with the if ''expression'' with {{{ if location == 'Poughkeepsie, NY': }}} and run it again. What happens? It should print "Go away, we're out eating tacos". Why? If I was in Poughkeepsie, I'd be out eating tacos too. Yummmm, tacos. If you're writing your own code, you don't want to provide an ''else'', just omit the keyword `else:` and the indented block you want to run with it. For example: {{{ #!python medianSalary=98260 #Median annual salary of a software engineer in the US. Yes, really. salary=90000 if salary > medianSalary: print("Whohoo! Dinner's on you!") }}} ''Go [https://www.tutorialspoint.com/execute_python3_online.php here] and run the code above.'' It should print: {{{ }}} Yep, nothing was output. Nada. In this case, we used variables which were numbers, and a greater-than expression to compare them. Since the condition was `False`, nothing was printed. (Also note the text in the code that starts with a # sign. The pound sign and everything after it on that line is called a ''comment'', and its a way to put some notes in the code for yourself that the program doesn't see or run. The robotics team wants you to put comments in your code '''a lot'''--it makes the code easier for others to read and understand. And we like it when we can understand you. Now for a couple of other control structures that you should know... == For Loop: Stop Hitting Yourself! == The For loop control structure runs code repeats over a variable. Try running this one: {{{ #!python fruits = ['banana', 'apple', 'mango'] for fruit in fruits: print("Current fruit :", fruit) print("That's alotta fruit!") }}} It should output: {{{ Current fruit : banana Current fruit : apple Current fruit : mango }}} This example loops over an ''array'' (a fancy word for a list) of fruits, and prints each value out, each line starting with the text "Current fruit:". To better understand what's going on here, pretend that the For Loop is basically a big arrow. The first time the For loop runs, this arrow (called the ''index variable'') points to the first value in the ''array'', {{{banana}}}, which it then sets to be the value of the index variable ''fruit''. After it prints the message, the for loop senses through arcane magic that there are other values in fruits, so it just moves the arrow to the second value and so on. After the third fruit, the for loop knows there's nothing left in fruits so it stops and the prints the last line "That's alotta fruit!" Note that the "Current fruit..." print statement is indented. Just like in the If-Then-Else control structure, you can run a block of of multiple lines of code in a for loop--just indent all the lines. For loops are handy if you want to avoid repeating yourself in code, and/or do the same thing over and over again. The less code you write, after all, the less chance you can make a mistake. Not to mention its easier to read. == While Loop: One more time around the block, Alfred! == A While loop is the more charming cousin of the For loop, this one repeats as long as its expression evaluates to ''True''. This expression is evaluated at the start of each loop, so it possible to not even run the While loop at all if expression starts out False. {{{ #!python count = 0 while (count < 9): print ("The count is:", count) count = count + 1 count = count + 1 # Yup, lets do it again because we're E-VIL print("Good bye!") }}} ''Go [https://www.tutorialspoint.com/execute_python3_online.php here] and run the code above.'' It should print {{{ }}} Since we're getting pretty far into these lessons, I'm not going to tell you the answer for this one. You should be seeing a pattern by now. What should it print? The count starts out at 0, and as long as count is less than 9 it will run the code in the block, then it will print "Good bye!". What else does it print out? == Compound Control Structures: Here a Control Structure, There a Control Structure, Everywhere a Control Structure... == Lastly, you can combine all three of these in any sort of combination, and even nest them. This is how you do real work in a program. For example, try running this one: {{{ #!python count=1 while (count<=7): if (count==4): print("more!") else: print(count, "potato,") count+=1 print("score!") }}} What does it output? See how the indenting works when nesting? Note that `count+=1` is shorthand for `count=count+1` because not typing those extra characters __could save your life someday__. Now, your turn: modify the code to make it repeat the word potato each time based on the current value of count, and run it. When you're done, the output should look like: {{{ 1 potato 2 potato potato 3 potato potato potato more! 4 potato potato potato potato 5 potato potato potato potato potato 6 potato potato potato potato potato potato 7 potato potato potato potato potato potato potato score! }}} Yeah, this is a little harder, but I bet you can do it. Ask a neighbor for help if you need to. I'll give you three hints: 1. You can tell a print to not end with a new line by adding an end="" to the print statement like this `print("I'm a teapot!",end="")`''. '' 1. An empty print statement `print("")` just prints a new line, basically the equivalent of having the program hit