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Variables

Python · Unit 1: First steps

A variable stores a value under a name. You create it with =: the name on the left, the value on the right.

To use it, write its name without quotes.

name = "Emma"
age = 17
print(name, "is", age)

Prints

Emma is 17

To change the value, use = again: the new one replaces the old one.

You can even use the current value to work out the new one.

points = 10
points = 25
print(points)
points = points + 5
print(points)

Prints

25
30

Names go in lowercase and use an underscore instead of spaces: my_age.

They can have numbers, but can't start with one, and they take no dashes.

my_age = 17
total_price = 250
print(my_age, total_price)

Prints

17 250

b = a copies into b the value that a has at that moment.

After that they're independent: if you change a, b stays the same.

today = 20
yesterday = today
today = 25
print(yesterday, today)

Prints

20 25

Exercises in this lesson

You do them in the app, which checks them on the spot and explains why.

  1. 1. Predict the output

    What does this code print?

    fruit = "apple"
print("fruit")
print(fruit)

  2. 2. Put the lines in order

    Order the lines to say hello to Emma.

  3. 3. Complete the code

    Fill in to create the variable the greeting uses.

    ___ = "Owen"
print("Hello,", name)

  4. 4. Predict the output

    What does this code print?

    weather = "sunny"
print("Today:", weather)
weather = "rainy"

  5. 5. Complete the code

    Noah won 5 more points. Fill in so his score goes up.

    points = 20
points = ___ + 5
print(points)

  6. 6. Find the bug

    This program should subtract the discount from the price. Which line has the error?

    price = 100
discount = 20
total = price + discount
print("Total to pay:", total)

  7. 7. Multiple choice

    Which one is a valid variable name in Python?

  8. 8. Find the bug

    This program should print Sophie's final grade. Which line has the error?

    final grade = 9
print("Grade:", final_grade)

  9. 9. Predict the output

    What does this code print?

    x = 5
y = x
x = 10
print(y)

  10. 10. Multiple choice

    What happens on the last line?

    mug = "tea"
glass = "coffee"
mug = glass

  11. 11. Find the bug

    Jack had 50 and spent 15. The program should print how much he has left. Which line has the error?

    money = 50
before = money
money = money - 15
print("Left:", before)

  12. 12. Predict the output

    Follow each variable line by line. What does it print?

    a = "red"
b = "blue"
c = a
a = b
b = c
print(a, b)
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