Variables and Data Types in Python

In Python, variables are used to store values, and data types define the kind of values stored in variables.
 
1. What is a Variable?
A variable is like a container that holds data. It allows us to store and reuse values in a program.
Declaring a Variable
In Python, you don’t need to specify the data type. Just assign a value to a variable using =.
name = "Alice"  # A string variable
age = 25        # An integer variable
height = 5.8    # A floating-point variable
is_student = True  # A boolean variable
print(name)   # Output: Alice
print(age)    # Output: 25
 
2. Rules for Naming Variables
Can contain letters (A-Z, a-z), digits (0-9), and underscores (_).
Cannot start with a number (e.g., 1name is invalid).
Case-sensitive (name and Name are different).
Should not use Python keywords like if, for, print, etc.
Use descriptive names (e.g., student_name instead of s).

my_var = 10       # Valid
_myVar = "Hello"  # Valid
2nd_var = 20      # Invalid (cannot start with a number)
class = "Math"    # Invalid (class is a Python keyword)
3. Data Types in Python
Python has several built-in data types:
x = 10         # Integer
y = 3.14       # Float
name = "Bob"   # String
is_valid = True  # Boolean
fruits = ["apple", "banana", "cherry"]  # List
person = {"name": "Alice", "age": 25}   # Dictionary
4. Checking Data Types
Use the type() function to check the type of a variable.
a = 100
b = 5.5
c = "Hello"
print(type(a))  # Output: <class 'int'>
print(type(b))  # Output: <class 'float'>
print(type(c))  # Output: <class 'str'>
 
5. Type Casting (Converting Between Data Types)
Python allows converting data from one type to another.
num = 10
num_str = str(num)  # Convert integer to string
num_float = float(num)  # Convert integer to float
print(num_str)  # Output: '10'
print(num_float)  # Output: 10.0
print(type(num_str))  # Output: <class 'str'>
print(type(num_float))  # Output: <class 'float'>
Common Conversions:
int(x) → Convert x to an integer
float(x) → Convert x to a float
str(x) → Convert x to a string
 
Summary
A variable is a name used to store a value.
Python supports multiple data types, including numbers, text, lists, and dictionaries.
Use the type() function to check the type of a variable.
You can convert data types using int(), float(), and str().