Python - Variables, Reserved Words & Data Types

1.Variables in Python

A variable is a name used to store a value in a program. In Python, we don't need to declare the variable type explicitly. Python automatically identifies the type of value.

Example

`name = "Gowtham"
age = 20
price = 99.5

print(name)
print(age)
print(price)`

Output:

Gowtham
20
99.5

In this example:

• name stores a string value.
• age stores an integer value.
• price stores a floating-point value.
• Rules for Naming Variables
• A variable name can contain letters, numbers, and underscores.
• A variable name must not start with a number.
• Variable names are case-sensitive.
• Spaces are not allowed in variable names.

• Reserved words cannot be used as variable names.

• Valid variable names:
  name = "Python"
  age = 20
  student_name = "Ravi"

• Invalid variable names:
  2name = "Ravi" # Starts with a number
  student name = "Ravi" # Contains a space
  class = 10 # Reserved word

2.Reserved Words in Python

Reserved words, also called keywords, are words that have special meanings in Python. They are used to define the structure and behavior of a program.

We cannot use these keywords as variable names or function names.

Common Python Keywords

3.Data Types in Python

A data type specifies the kind of value stored in a variable. Python provides several built-in data types.

1.Numeric Types

Integer (int) — Stores whole numbers.

age = 20
print(age)

Float (float) — Stores decimal numbers.

price = 99.5
print(price)

Complex (complex) — Stores complex numbers.

number = 2 + 3j
print(number)

2.String (str)

A string stores text inside single or double quotation marks.

name = "Python"
print(name)

Output:

Python

3.Boolean (bool)

A Boolean represents either True or False.

is_student = True
print(is_student)

Output:

True

4.List (list)

A list stores multiple items in a single variable. Lists are ordered and mutable, meaning their contents can be changed.

fruits = ["apple", "banana", "mango"]
print(fruits)

5.Tuple (tuple)

A tuple stores multiple items. Unlike lists, tuples cannot be changed after creation.

colors = ("red", "green", "blue")
print(colors)

6.Set (set)

A set stores unique values and does not guarantee a fixed order.

numbers = {1, 2, 3, 3}
print(numbers)

The duplicate value 3 is stored only once.

7.Dictionary (dict)

A dictionary stores information as key-value pairs.

`student = {
"name": "Ravi",
"age": 20
}

print(student["name"])`

Output:

Ravi

8.None Type (NoneType)

None represents the absence of a value.

result = None
print(result)

Output:

None