what does "by value or by reference" mean in python programming

 In Python, arguments to functions are passed by reference, but in a slightly nuanced way. Here's a breakdown:

• By Value: In some languages, when you pass an argument to a function, a copy of the argument's value is created. Changes made to the argument within the function do not affect the original variable outside the function.

• By Reference: In other languages, when you pass an argument to a function, you're essentially passing a memory address. Changes made to the argument within the function do affect the original variable outside the function.

• Python's Approach: Python uses a mechanism that's often described as "pass-by-object-reference."

  • For immutable objects (like numbers, strings, tuples): It behaves like pass-by-value. Changes made to the argument within the function create a new object, leaving the original object unchanged.

  • For mutable objects (like lists, dictionaries): It behaves more like pass-by-reference. Changes made to the argument within the function can affect the original object.

Example:

Python

# Immutable object (string)
def modify_string(s):
    s = s + " World" 

my_string = "Hello"
modify_string(my_string)
print(my_string)  # Output: "Hello" (original string unchanged)

# Mutable object (list)
def modify_list(lst):
    lst.append(4)

my_list = [1, 2, 3]
modify_list(my_list)
print(my_list)  # Output: [1, 2, 3, 4] (original list modified)

Key takeaway:

While Python doesn't strictly adhere to either pass-by-value or pass-by-reference, understanding the concept of immutability is crucial. For immutable objects, changes within a function don't affect the original object. For mutable objects, changes can potentially affect the original object.