In Python, everything is an object and arguments are passed to functions as object references, not as actual values or references to the memory location of values (as in some other languages). This behavior can sometimes be misconstrued as passing by value or passing by reference, but it's more accurate to say Python uses a mechanism best described as "pass by object reference".
When arguments are passed to functions in Python, the behavior regarding mutability and immutability of these arguments can be a source of confusion. Let's delve deeper into how Python handles both immutable and mutable types when passed to functions:
1. Passing Immutable Types to Functions:
Immutable types in Python include basic data types like `int`, `float`, `str`, and `tuple`. "Immutable" means that the state or content of these types cannot be modified after they are created.
When an immutable type is passed to a function, any modification to that argument within the function's scope does not affect the original object in the caller's scope.
def modify_value(x):
x += 10
print("Inside function:", x)
num = 20
modify_value(num)
print("Outside function:", num)
# Outputs:
# Inside function: 30
# Outside function: 20
In this example, the integer `num` is unchanged outside the function, even though it appears to be modified inside the function.
2. Passing Mutable Types to Functions:
Mutable types in Python include data structures like `list`, `dict`, `set`, and some custom objects. These types can have their content modified or adjusted after creation.
When a mutable type is passed to a function, changes to that argument within the function do affect the original object in the caller's scope.
def modify_list_content(lst):
lst.append("apple")
print("Inside function:", lst)
fruits = ["banana", "cherry"]
modify_list_content(fruits)
print("Outside function:", fruits)
# Outputs:
# Inside function: ['banana', 'cherry', 'apple']
# Outside function: ['banana', 'cherry', 'apple']
In this scenario, the list `fruits` is altered both inside and outside the function.
