02-02: Variables and Data Types¶

What is a Variable?¶

A variable can be thought of as a label attached to a value.

It represents a named reference to data stored in memory, allowing that data to be accessed and modified throughout a program.

x = 10
name = "Imran"

x refers to the integer value 10

name refers to the string value "Imran"

Rules for Naming Variables¶

✅ Valid Examples¶

age = 25
user_name = "John"
_marks = 90

❌ Invalid Examples¶

2age = 25      # cannot start with a number
user-name = 10 # hyphen not allowed
3 = num        # not allowed, variable has to be on the left
_3 = 10        # legal, but not recommended

🔹 Naming Rules¶

Only letters (a–z, A–Z), digits (0–9), and underscore (_) are allowed in variable names
A variable name must begin with a letter or an underscore (_)
A variable name cannot begin with a digit
Spaces and special characters (except underscore) are not allowed
Variable names are case-sensitive (age and Age are different)

Assigning Values to Variables¶

Values are assigned using the = operator.

a = 5
b = 3.14
c = "Hello"

Python automatically determines the data type of the assigned value.

🔄 Multiple Assignment¶

Multiple variables can be assigned values in a single statement.

x, y, z = 1, 2, 3

It is also possible to assign the same value to multiple variables:

a = b = c = 10

Basic Data Types in Python¶

1️⃣ Integer (int)¶

Represents whole numbers.

x = 10
y = -5

2️⃣ Float (float)¶

Represents decimal numbers.

pi = 3.14
temp = -2.5

3️⃣ String (str)¶

Represents textual data enclosed in quotes.

name = "Imran"
msg = 'Hello World'

4️⃣ Boolean (bool)¶

Represents logical values: True or False.

is_active = True
is_logged_in = False

Checking Data Type¶

The type() function is used to determine the data type of a variable.

x = 10
print(type(x))

👉 Output:

<class 'int'>

Type Conversion (Casting)¶

Type conversion is used to convert a value from one data type to another.

x = "10"     # data type string

Convert string to integer¶

y = int(x)

Convert integer to float¶

z = float(y)

Putting it together:

x = "10"
y = int(x)
z = float(y)

print(y, type(y))
print(z, type(z))

👉 Output:

10 <class 'int'>
10.0 <class 'float'>

⚠️ Important Notes: 🔹 Dynamic Typing¶

Python is a dynamically typed language, meaning a variable can refer to different data types during execution.

x = 10      # integer
x = "Hello" # now a string

print(x, type(x))

👉 Output:

Hello <class 'str'>

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Exercises: 02-02: Exercises — Variables and Data Types

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