Variables and Data Types

In Python, variables are names that can be assigned a value and then used to refer to that value throughout your code. Variables are fundamental to programming for two reasons:

1. Variables keep values accessible: For example, you can assign the result of some time-consuming operation to a variable so that your program doesn’t have to perform the operation each time you need to use the result.

2. Variables give values context: The number 38 could mean lots of different things, such as the number of students in a class, the number of times a user has accessed a website, and so on. Giving the value 38 a name like num_students makes the meaning of the value clear.

Variable names are case sensitive, so a variable named greeting is not the same as a variable named Greeting. For instance, the following code produces a NameError:

greeting = "Hello, World"
print(greeting)

## Hello, World

Rules for Valid Variable Names

Variable names can be as long or as short as you like, but there are a few rules that you must follow. Variable names may contain uppercase and lowercase letters (A–Z, a–z), digits (0–9), and underscores (_), but they cannot begin with a digit. For example, each of the following is a valid Python variable name:

• string1

• _a1p4a

• list_of_names

The following aren’t valid variable names because they start with a digit:

• 9lives

• 99_balloons

• 2beOrNot2Be

Descriptive variable names are essential, especially for complex programs. Writing descriptive names often requires using multiple words.For example s=1000 and seconds=1000.seconds is a better name than s because it provides more context.

s=1000
seconds=10000

DATA TYPES

Python has several built-in data types used to store different kinds of values.

1.Numeric types

int — Integer

Used for whole numbers.

age = 20
marks = 85
temperature = -5

print(age)

## 20

print(type(age))

## <class 'int'>

print(type(marks))

## <class 'int'>

float — Decimal Number

Used for numbers containing decimals.

price = 99.50
height = 1.75

print(price)

## 99.5

print(type(price))

## <class 'float'>

complex — Complex Number

Contains a real and imaginary part.

z = 3 + 4j

print(z)

## (3+4j)

print(z.real)

## 3.0

print(z.imag)

## 4.0

print(type(z))

## <class 'complex'>

2. Boolean Type

bool Stores either True or False.

is_student = True
is_logged_in = False

print(is_student)

## True

print(type(is_student))

## <class 'bool'>

Booleans are commonly used in conditions:

age = 20

if age >= 18:
    print("Adult")
else:
    print("Minor")

## Adult

3. String Type

str

Used to store text.

name = "John"
message = 'Hello Python'

print(name)

## John

print(type(name))

## <class 'str'>

4. List Type

list

A list stores multiple values and is ordered and changeable (mutable).

fruits = ["apple", "banana", "orange"]

print(fruits)

## ['apple', 'banana', 'orange']

print(fruits[0])

## apple

5. Tuple Type

tuple A tuple is ordered but cannot be changed (immutable).

coordinates = (10, 20)

print(coordinates)

## (10, 20)

print(coordinates[0])

## 10

6. Set Type

set

A set stores unique values and does not maintain normal index-based access.

numbers = {1, 2, 3, 4, 4, 5}

print(numbers)

## {1, 2, 3, 4, 5}

The duplicate 4 is removed.

You can add values:

numbers.add(6)
print(numbers)

## {1, 2, 3, 4, 5, 6}

a = {1, 2, 3}
b = {3, 4, 5}

print(a | b)  # Union

## {1, 2, 3, 4, 5}

print(a & b)  # Intersection

## {3}

7. Dictionary Type

dict

A dictionary stores data as key-value pairs.

student = {
    "name": "John",
    "age": 20,
    "course": "Python"
}

print(student)

## {'name': 'John', 'age': 20, 'course': 'Python'}

print(student["name"])

## John