Python Variables: How to Store and Use Values

Programs need to remember things: a user's name, a score, the price of an item. A variable is a name that refers to a value, so you can use and change that value later.

Creating a variable#

You create a variable by writing a name, an equals sign, and a value:

city = "Mumbai"
temperature = 31

print(city)
print(temperature)

Mumbai
31

The = here is the assignment operator. Read temperature = 31 as "temperature now refers to 31", not as "temperature equals 31" in the maths sense. Python takes the value on the right and attaches the name on the left to it.

Using variables in calculations#

Once a value has a name, you can use the name anywhere you would use the value:

price = 250
quantity = 4
total = price * quantity

print(total)

1000

Changing a variable#

Assigning again replaces the old value:

score = 10
print(score)

score = 15
print(score)

score = score + 5
print(score)

10
15
20

score = score + 5 looks strange at first. Python always works out the right side first (current score 15 plus 5 is 20), then stores the result back in score.

There is a shorter way to write this, called an augmented assignment:

score = 20
score += 5   # same as score = score + 5
score -= 3   # same as score = score - 3
score *= 2   # same as score = score * 2
print(score)

44

Variables can change type#

A variable is just a label, so the same name can point to a different kind of value later:

answer = 42
answer = "forty-two"
print(answer)

forty-two

This is allowed, but doing it on purpose usually makes code confusing. Keep each variable holding one kind of value.

Naming rules#

Python enforces a few rules:

• Names can contain letters, digits, and underscores (_).
• Names cannot start with a digit: 2nd_place is invalid, second_place is fine.
• Names cannot contain spaces or hyphens: user name and user-name are invalid.
• Names are case-sensitive: age and Age are different variables.
• You cannot use Python's reserved words such as if, for, class, True, or None.

Naming conventions#

Beyond the rules, Python programmers follow a style guide called PEP 8. For variables it recommends snake_case: all lowercase, with words separated by underscores.

Assigning several variables at once#

x, y, z = 1, 2, 3
print(x, y, z)

a = b = 0
print(a, b)

1 2 3
0 0

This also gives Python a famously neat way to swap two values:

first = "left"
second = "right"
first, second = second, first
print(first, second)

right left

Putting variables into text with f-strings#

The easiest way to mix variables into text is an f-string. Put an f before the opening quote and wrap variable names in curly braces:

name = "Priya"
items = 3
total = 749.5

print(f"{name} bought {items} items for ₹{total}")
print(f"Average price: ₹{total / items:.2f}")

Priya bought 3 items for ₹749.5
Average price: ₹249.83

You can put any expression inside the braces. The :.2f part formats the number with exactly two decimal places.

Common mistakes#

Practice#

price = 45
quantity = 6

total = price * quantity
discounted_total = total * 0.9

print(f"{quantity} notebooks cost ₹{discounted_total:.2f} after discount")

6 notebooks cost ₹243.00 after discount

Key takeaway#