Python Variables

A variable is a name that refers to a value in a Python program.

Variables allow us to store information and use that information later in our program.

For example, instead of writing the number 25 repeatedly, we can store it in a meaningful variable called age.

age = 25

print(age)

25

Here, age is the variable name and 25 is the value assigned to it.

Python does not require a special command to declare a variable.

A variable is created when you assign a value to a name using the assignment operator =.

name = "Adnan"
age = 30
salary = 75000.50
is_student = False

Python automatically determines the type of value being assigned.

Beginners often imagine a variable as a physical box containing a value.

This is a useful beginner-friendly model, but Python's actual behavior is better understood as a name referring to an object.

x = 10
y = x

print(x)
print(y)

10
10

Both x and y refer to the value 10.

You do not normally need to worry about Python's memory management at this stage, but understanding that variables are names referring to objects becomes very useful as you progress to lists, dictionaries, functions and object-oriented programming.

A variable can be assigned a new value at any time.

score = 50

print(score)

score = 80

print(score)

50
80

The second assignment changes what score refers to.

Updating a Value

You can also calculate a new value using the existing variable.

score = 50

score = score + 10

print(score)

60

Python allows you to assign values to multiple variables in a single statement.

name, age, city = "Ali", 25, "Multan"

print(name)
print(age)
print(city)

Ali
25
Multan

Python matches the values from left to right with the variable names.

You can assign the same value to several variables at once.

x = y = z = 0

print(x)
print(y)
print(z)

0
0
0

This can be convenient when several variables need the same initial value.

A Python variable can refer to many different kinds of objects.

name = "Sara"
age = 22
height = 5.6
is_student = True

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

<class 'str'>
<class 'int'>
<class 'float'>
<class 'bool'>

The built-in type() function tells us the type of object referenced by a variable.

Python has specific rules for naming variables.

• A variable name can contain letters, numbers and underscores.
• A variable name cannot start with a number.
• A variable name cannot contain spaces.
• A variable name is case-sensitive.
• Python keywords cannot be used as variable names.

Valid Names

name = "Ahmed"
age = 25
user_name = "Ahmed"
score2 = 90
_private_value = 100

Invalid Names

2name = "Ahmed"
user name = "Ahmed"
user-name = "Ahmed"

Python programmers commonly use snake_case for variable names.

first_name = "Ahmed"
last_name = "Khan"
total_price = 1500
customer_age = 28

Snake case separates words using underscores. It makes longer variable names easier to read.

Meaningful Names

Choose names that communicate what the variable represents.

student_name = "Hassan"
exam_score = 87
monthly_salary = 85000

Python variable names are case-sensitive.

This means name, Name and NAME are three different names.

name = "Ali"
Name = "Ahmed"
NAME = "Sara"

print(name)
print(Name)
print(NAME)

Ali
Ahmed
Sara

Python is a dynamically typed language. You do not need to declare the type of a variable before assigning a value.

A variable can also later refer to an object of a different type.

value = 100

print(type(value))

value = "Python"

print(type(value))

<class 'int'>
<class 'str'>

The name value first refers to an integer object and later refers to a string object.

Python does not have a special keyword that makes a variable permanently constant.

However, programmers commonly use UPPERCASE names to indicate that a value should not normally be changed.

PI = 3.14159
MAX_LOGIN_ATTEMPTS = 5
COMPANY_NAME = "PyLearn"

These names communicate programmer intent. Python will not prevent you from assigning a new value to them.

1. Starting With a Number

1student = "Ali"

Variable names cannot begin with a number.

2. Using Spaces

student name = "Ali"

Use underscores instead: student_name.

3. Forgetting Case Sensitivity

student_name = "Ali"

print(Student_name)

Student_name is different from student_name.

4. Using Unclear Names

x = 45000

If the value represents a salary, this is much clearer:

monthly_salary = 45000

Variables are one of the most fundamental concepts in Python. They allow programs to store, access and work with information.

• A variable is a name that refers to an object.
• Variables are created using the assignment operator =.
• Python does not require explicit variable declarations.
• Variables can be reassigned new values.
• Python supports multiple assignment.
• Python variable names are case-sensitive.
• Variable names cannot begin with numbers or contain spaces.
• snake_case is the common naming style for Python variables.
• Python uses dynamic typing.
• Uppercase names are commonly used by convention for constants.