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Python Tutorial › Basics › Variables

Python Variables

BeginnerLesson 8 of 4710 min read10 runnable examples

A variable is a name that refers to a value, so you can use the value later, change it, and make your code readable. In Python you create a variable simply by assigning to it.

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In this lesson
  • Create and update variables
  • Follow Python’s naming rules
  • Assign several variables at once
  • Understand that names point to objects

Create a variable

Write a name, an equals sign and a value. Python creates the variable the first time you assign to it. There is no var, let or type declaration.

Python
browser = "chromium"timeout = 30headless = True print(browser, timeout, headless)
Output
chromium 30 True
Note

= means assign, not “is equal to”. timeout = 30 stores 30 under the name timeout. To compare two values you use ==, covered in Operators.

Change a variable

Assigning again replaces the old value. The new value can even be a different type, because Python variables do not have a fixed type; the value does.

Python
count = 1count = count + 1      # read the old value, add 1, store the resultcount += 1             # the same thing, written shorterprint(count) count = "three"        # now it holds a stringprint(count, type(count))
Output
3
three <class 'str'>

Naming rules

RuleValidInvalid
Letters, digits and underscores onlyuser_2user-2, user 2
Cannot start with a digit_2nd, second2nd
Cannot be a keywordclass_nameclass, for
Case-sensitivetotal and Total are different
Python
user-name = "asha"
Output
  File "main.py", line 1
    user-name = "asha"
    ^^^^^^^^^
SyntaxError: cannot assign to expression here. Maybe you meant '==' instead of '='?

Naming conventions

These are not enforced by Python but every Python developer follows them (they come from the PEP 8 style guide):

  • snake_case for variables and functions: max_retries, page_title.
  • UPPER_CASE for constants that should not change: BASE_URL, MAX_RETRIES.
  • PascalCase for classes: LoginPage.
  • Use names that say what the value means: retries beats r, price_in_rupees beats p.

Assign several variables at once

Python
x, y, z = 10, 20, 30           # one value per nameprint(x, y, z) a = b = c = 0                  # the same value to every nameprint(a, b, c) first, *rest = [1, 2, 3, 4]    # * collects the leftovers into a listprint(first, rest)
Output
10 20 30
0 0 0
1 [2, 3, 4]

The number of names on the left must match the number of values, unless one name has *:

Python
x, y = 1, 2, 3
Output
Traceback (most recent call last):
  File "main.py", line 1, in <module>
    x, y = 1, 2, 3
    ^^^^
ValueError: too many values to unpack (expected 2, got 3)

Swap two variables

Many languages need a temporary variable to swap. Python swaps in one line:

Python
a = 10b = 20a, b = b, aprint("a =", a, "b =", b)
Output
a = 20 b = 10

Variables are names for objects

A variable does not contain the value; it refers to an object in memory. Two names can refer to the same object. id() shows an object’s identity and is checks whether two names refer to the same object.

Python
scores = [90, 85]backup = scores           # a second name for the same listbackup.append(70) print(scores)print(backup is scores)
Output
[90, 85, 70]
True

This is why changing a list through one name shows up through the other. Numbers and strings cannot be changed in place, so for them this never surprises you:

Python
a = 5b = ab = b + 1      # creates a new int object; a still refers to 5print(a, b)
Output
5 6
Tip

The Lists lesson shows how to make a real copy with .copy() when you need one.

Delete a variable

del removes a name. Using the name afterwards raises NameError.

Python
temp = 42del tempprint(temp)
Output
Traceback (most recent call last):
  File "main.py", line 3, in <module>
    print(temp)
          ^^^^
NameError: name 'temp' is not defined

Constants

Python has no true constants. By convention a name in UPPER_CASE tells other developers “do not change this”:

Python
BASE_URL = "https://sqatools.in"MAX_RETRIES = 3 for attempt in range(1, MAX_RETRIES + 1):    print(f"Attempt {attempt} of {MAX_RETRIES} on {BASE_URL}")
Output
Attempt 1 of 3 on https://sqatools.in
Attempt 2 of 3 on https://sqatools.in
Attempt 3 of 3 on https://sqatools.in

Check your understanding

Predict the output

a = 3b = aa = a * 2print(a, b)

Quick quiz

1. Which is a valid Python variable name?

2. What does x, y = y, x do?

3. What is the convention for a value that should never change?

4. What does first, *rest = [5, 6, 7] put in rest?

Exercise: shopping cart total

Store the item price, quantity and discount percentage in well-named variables, then print the final amount.

Input
price = 250, quantity = 4, discount = 10%
Expected output
Subtotal: 1000
Final amount: 900.0
Hint 1

The discount amount is subtotal * discount_percent / 100.

Program Practice

40 Python Basic Programs

Every program has a step-by-step explanation, colour-coded code and its real output.

Start practising →
#1EasyAdd two integers#2EasySubtract two integers#3EasyMultiply two numbers#4EasyRepeat a string 5 times#5EasyAverage of given numbers#6MediumMedian of given numbers
Related sets:All practice sets

Python variables FAQ

Do I need to declare a variable type in Python?

No. Python works out the type from the value you assign. n = 5 is an int and n = "5" is a str. You can add optional type hints, such as n: int = 5, for readability.

How do I swap two variables in Python?

Use tuple unpacking: a, b = b, a. No temporary variable is needed.

What is the difference between = and ==?

= assigns a value to a name. == compares two values and returns True or False.

Can a variable name start with an underscore?

Yes. A single leading underscore, as in _cache, is a convention meaning “internal, do not use from outside”.

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