Year 8 · Spring 2 · Python I

Variables, data types and arithmetic

What this lesson covers

Topic 13 Programming basics

KS3 Computing · A program stores information in variables, works on it with operators, and controls the order with sequence, selection and iteration. Examples are in Python, with Scratch alongside for Year 7.

ProgrammingCambridge Lower Secondary Computing 0860

You will learn to

Explain what a variable is, and read = as 'becomes'.
Identify int, float and str values, like 7, 3.5 and "7".
Use int() to turn typed input into a number before doing maths.
Use // and % to work out DIV and MOD, like 17 // 5 = 3 and 17 % 5 = 2.

Success criteria

I can read score = score + 10 aloud as 'score becomes score plus 10'.
I can explain why "7" + "7" gives "77", but 7 + 7 gives 14.
I can build a tiny calculator that adds two numbers the user types.

Key words

Say each word, then read what it means. Every one is in the glossary too.

variable: A named place in memory that holds a value.
assignment: Storing a value in a variable. = in Python, ← in pseudocode.
concatenation: Joining strings together: "7" + "7" = "77".
Casting: Changing a value from one data type to another, like int("13").
Selection: Choosing a path with if / else.
Iteration: Repeating steps: a loop.
Boolean: A value that is only True or False.
Infinite loop: A loop whose condition never becomes false.

The explanation

Read it here, or open the study page below to go one step at a time with things to try.

Variables: labelled boxes

A variable is a named box in memory that holds a value.

score = 0
score = score + 10
print(score)

score = 0: make a box called score, put 0 in it. This is assignment.
score = score + 10: read the right side first. 0 + 10 = 10. Put 10 back in the box.
print(score) shows 10.

!Watch out

In code, = means 'store', not 'equals'. To ask if two things are equal, use ==.

e.g.Example

Scratch: the orange 'set score to 0' and 'change score by 10' blocks.

Data types

Type	Holds	Python examples
Integer (`int`)	Whole numbers	7, -3, 0
Float (`float`)	Decimal numbers	3.14, 0.5
String (`str`)	Text in quotes	"Hello", "7"
Boolean (`bool`)	True or False	True, False

!Watch out

"7" in quotes is text. 7 + 7 gives 14, but "7" + "7" gives 77 (joining text, called concatenation).

Arithmetic operators

Operator	Meaning	Example	Result
+	Add	7 + 2	9
-	Subtract	7 - 2	5
*	Multiply	7 * 2	14
/	Divide	7 / 2	3.5
//	Whole-number divide (DIV)	7 // 2	3
%	Remainder (MOD)	7 % 2	1
**	Power	2 ** 8	256

e.g.Example

n % 2 == 0 checks if a number is even.

Study it

Open the study page and go one step at a time.

Topic 13 · Year 8

Programming basics

A program stores information in variables, works on it with operators, and controls the order with sequence, selection and iteration. Examples are in Python.

The steps for this lesson

Topic 13, step 2: Variables (Watch the variable boxes)
Topic 11, step 5: Four ways to write it (DIV and MOD)

Try it

Check yourself

One question at a time. The reason shows after each answer.

Saved on this device.