Lockers with labels

Picture a row of lockers at college. Each locker has a name on the door. Inside is one thing.

A program stores data in the same way. Each place has a name. Inside is a value. The name lets you find the value again.

Key words

Word	What it means	Example
Variable	A name that holds a value. The value can change.	score = 10
Constant	A name that holds a value that never changes.	PI = 3.14
Declare	Create a variable or constant and give it a first value.	age = 16
Assignment	Putting a value into a variable. Python uses the = sign.	score = 0
Data type	The kind of value, such as a whole number or text.	integer, string
Integer	A whole number.	42
Float	A number with a decimal point.	2.5
String	Text inside quote marks.	"Sam"
Boolean	True or False.	True

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Try it: make a variable

Code: python

name = "Sam"
age = 16
height = 1.75
is_student = True

print(name)
print(age)
print(height)
print(is_student)

# Change the values and press Run.

What is a variable?

A variable is a name that holds a value. The value can change while the program runs.

You make a variable by writing its name, then =, then the value. This is called declaring it. Python finds the data type from the value.

The variables in the code above

Name	Value	Data type
name	"Sam"	String
age	16	Integer
height	1.75	Float
is_student	True	Boolean

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The = sign is not "equal to"

data-callouts.warning.label

In Python, = means "put this value into this name". It copies the value from the right into the name on the left. Two equals signs, ==, ask a question. You meet that later.

Try it: change a variable

Code: python

score = 0
print(score)

score = score + 10
print(score)

score = score + 10
print(score)

# The value changes each time.
# Add one more line that adds 5.

Rules for a good name

Rule	Good	Not allowed or poor
Use letters, numbers and underscores.	total_score	total-score
Never start with a number.	player1	1player
No spaces.	first_name	first name
Capital letters make a different name.	Score and score are two names	Using both by mistake
Choose a name that says what it holds.	ticket_price	x

The cells students fill in are left blank in this preview.