Variables:

A variable is a reference or name that points to an object in memory. Variables themselves don’t hold the actual data but they point to objects that holds data. In Python, when you assign a variable, it just holds a reference to an object.

Rules for naming variables:

• Allowed Characters: Letters (a-z, A-Z), digits (0-9), and underscores (_).

• Variable names can’t start with a number.

• Case Sensitive: var, Var, and VAR are different variables.

• No Reserved Keywords: Python keywords (like for, if, while, etc.) cannot be used as variable names

# Valid variable names
my_name = "unknown"
_age = 25

# Invalid variable names
 2name = "rocky"  # Starts with a number
 for = "hello"    # 'for' is a reserved keyword

Variable Scope:

Scope defines where a variable can be accessed in the code

Global Variable:

Defined outside any function and can be accessed anywhere in the program.

Local Variable:

Defined inside a function and only accessible within that function.

# Global variable
x = 100
def example_function():
    # Local variable
    y = 500
    print("Inside function, y:", y)   #Inside function, y:500
    print("Inside function, x (global):", x)  # Can access global x

 example_function()
 print("Outside function, x:", x)  #Outside function, x:100
 print(y)  # Error! y is not accessible outside the function

Modifying Global Variables:

#  Modifying Global Variables:
# To modify a global variable inside a function, you need to use the global keyword.
x = 10  # Global variable

def modify_global():
     global x
     x = 20  # Modify the global variable

modify_global()
print(x)  # Output: 20

Multiple Assignment:

Python allows you to assign multiple variables at once. This can be useful when you need to assign multiple values or swap values between variables.

# Multiple variables assigned at once
 a, b, c = 1, 2, 3
 print(a, b, c)  # Output: 1 2 3

 a=b=c=12
 print(a, b, c)  # Output: 12 12 12

# Swapping variables
 x, y = 10, 20
 x, y = y, x  # Swap x and y
 print(x, y)  # Output: 20 10

Unpacking Variables:

You can unpack values from sequences (such as lists or tuples) into variables

# Unpacking a list
 numbers = [1, 2, 3]
 a, b, c = numbers
 print(a, b, c)  # Output: 1 2 3

# Unpacking a tuple
 var = (10, 20)
 x, y = var
 print(x, y)  # Output: 10 20

Comments:

Not executed ,used for understanding or documenting the code

# single line comments
print(3+90)  #adding two numbers 

'''
multiple line
comments
'''

Input /Output :

input:

input( ) function is used to take i/p from user

output:

print( ) function is used to display output

name = input("enter your name:")  #by default input is taken as string
age = int(input("enter age:"))    #input data is integer
weight = float(input("weight:"))  #input data is decimal values
print(name)
print(type(name))     #string type data
print(age)
print(type(age))      #integer type data
print(weight)
print(type(weight))    #float type data