Glossary

Programming words, in plain language. New words get added as they come up in chapters. If a word here doesn’t make sense yet, don’t worry — it’ll show up in a session and click into place.

Words from later phases (web, etc.) get added when those phases start. So far this glossary covers Phase 1 (Scratch) and Phase 2 (Python with Turtle).

Phase 1 — Scratch words

Block The colorful pieces you snap together in Scratch. Each block is one instruction (move 10 steps, wait 1 seconds, etc.). Blocks have shapes that fit together — that’s how Scratch tells you what goes where.

Conditional A programming idea: “if something, then do this.” In Scratch, the if block. The “if” part is a question Scratch can answer with yes or no. If the answer is yes, the inside runs. If no, it doesn’t.

Costume A different look for a sprite. Many sprites have multiple costumes built in (like a cat with two different walking poses). Switching costumes is how sprites animate.

Event A thing that happens while a program is running — a key being pressed, a sprite being clicked, the green flag being clicked. Each event can trigger a script to run. Sprites can have many scripts, each listening for a different event.

Extension An extra category of blocks you can add to Scratch. The most useful one for Phase 1 is Pen, which lets sprites draw lines as they move. Add an extension by clicking the “Add Extension” button at the bottom-left of the Scratch window.

Forever A loop that runs its inside over and over until you click the red stop sign. Used a lot in games — “every fraction of a second, check the keyboard and update the cat’s position.”

If block The Scratch block that does conditional logic. Has a diamond- shaped slot at the top (for the question) and a mouth (for what to do if the answer is yes).

Loop A way to do something multiple times without writing it multiple times. Scratch has repeat N (do this N times) and forever (do this until I stop you).

Mouth The opening in some Scratch blocks (like repeat, forever, and if) where other blocks go inside. Things in the mouth run as part of the outer block.

Pen A Scratch extension that lets sprites draw as they move. pen down starts drawing; pen up stops. Used in Session 3 to draw shapes.

Script A stack of blocks that runs together, starting from the top (usually a “starter” block like when green flag clicked or when [key] pressed). One sprite can have many scripts; each one runs when its starter block triggers.

Sensing A category of Scratch blocks that check things in the world — “is the space key pressed?”, “am I touching another sprite?”, “what’s the mouse pointer’s x position?” Sensing blocks usually go inside if blocks.

Sequence A series of blocks that run one after another, top to bottom. The most basic kind of program. Order matters.

Sprite A character or object on the Scratch stage. The default sprite is the orange cat. Sprites have their own scripts, costumes, and position on the stage.

Stage The big rectangle in Scratch where sprites do their thing. The stage has a coordinate system: x goes left/right, y goes up/down, and (0, 0) is the middle. The stage is about 480 wide × 360 tall.

Variable A labeled box that holds a value (usually a number). You can put something in (set), change what’s in it (change), and read it back ((varname)). Used for things that change over time, like a score. Created with the “Make a Variable” button in the Variables category.

X position / Y position Where a sprite is on the stage. X is left-right (negative is left, positive is right). Y is up-down (negative is down, positive is up). The middle of the stage is x = 0, y = 0.

Phase 2 — Python words

Argument A value you pass to a function when you call it. In t.forward(100), the 100 is an argument — it’s the information the function uses. (See also: parameter.)

Comment Text starting with # that Python ignores. Used to leave notes in your code for yourself or other readers — like a label on a section of code. Comments don’t change what the program does.

Elif Short for “else if.” A way to check another condition after an if’s condition was false. You can chain as many elifs as you want before a final else (or no else at all).

Else The “otherwise” part of an if. The body under else runs when the if’s condition is false. Optional — you don’t always need one.

Error message What Python tells you in red text when something goes wrong. Error messages are trying to help. They usually tell you the file, the line number, and what kind of problem (SyntaxError, NameError, AttributeError, etc.). Read them slowly.

Float A number with a decimal point, like 5.0 or 3.14. Division in Python (/) always gives a float, even when the answer is whole (15 / 3 is 5.0, not 5).

For loop The Python version of Scratch’s repeat. for i in range(N): runs the indented body N times. The i is a loop variable that takes the values 0, 1, 2, …, N-1.

Function A named chunk of code you can call by name. You define it with def name(): and the indented body underneath. You call it by writing name() somewhere later. The biggest new idea in Phase 2.

IDE Short for Integrated Development Environment. A program for writing code. Thonny is an IDE. So are VS Code, PyCharm, and many others. We use Thonny in this class.

Import A Python statement that brings in a module (a toolbox of code written by someone else) so you can use it. import turtle brings in the turtle module so you can do t = turtle.Turtle().

Indentation Spaces at the start of a line. In Python, indentation is part of the grammar — it’s how Python knows which lines belong inside a for loop, if, def, etc. Lines indented underneath are “inside”; lines not indented are “outside.” Standard is 4 spaces.

Module A bundle of Python code you can import and use. Comes from Python’s standard library (like turtle) or from the internet (like Pygame, later in the class). Sometimes also called a library.

Operator A symbol that does something. Math operators: + - * /. Comparison operators: < > == != <= >=. The = sign is the assignment operator (gives a variable a value).

Parameter A placeholder name in a function definition. In def draw_square(size):, size is the parameter. When you call the function with draw_square(50), the parameter size gets the value 50 for that call. (See also: argument.)

Print A Python function (print(...)) that displays text or values in the shell. Useful for showing output to the user, and especially useful for debugging — print(size) shows what size is right now.

Python The programming language we use after Scratch. Real, general-purpose, used by professional developers, scientists, data analysts, web developers — almost everyone. We use it through Thonny.

range A built-in Python function that gives a sequence of numbers. range(5) is the numbers 0, 1, 2, 3, 4. Almost always used inside a for loop: for i in range(5): runs five times.

Run To execute your program. In Thonny, click the green Run button or press F5. Python reads your code top to bottom and does what it says.

Save To write your code to a file on your computer. Files end in .py. Save before you Run, or Thonny will sometimes complain. Use Ctrl-S as a shortcut.

Shell The bottom panel of Thonny. Where Python prints messages, where errors appear, and where you can type one-line Python experiments interactively (without saving a file).

SyntaxError A Python error that means “your code’s grammar is wrong.” Usually a missing colon, missing parenthesis, or wrong indentation. Python points at where it noticed the problem (which is sometimes a line after the actual mistake).

Thonny The Python editor we use in class. Has an editor (top), a shell (bottom), and a green Run button. Pre-installed on every class machine.

Turtle The Python module we use in Phase 2 to draw on the screen. Imported with import turtle. The turtle is a little arrow (or actual turtle shape) that moves around drawing lines.

General programming words

Bug A mistake in code that makes it do the wrong thing. Named after a real moth that got stuck in an early computer in 1947 and stopped it from working.

Code A general word for “instructions you wrote for the computer.” Scratch blocks are code. Python lines are code. HTML tags are code.

Debugging Fixing bugs. Half of programming.

Program A complete set of instructions that does something. Your Scratch projects are programs. So is every app on your phone.

Programmer A person who writes programs. Also: you, after about three weeks of class.

This glossary will grow as the curriculum moves into Python and beyond. If a word should be here and isn’t, ask Mr. Eric to add it.