Value Types and Reference Types in Python

In Python, data types can be divided into two main categories: value types and reference types

This is something common in many programming languages. Understanding the differences between both is very important (or you might elegantly mess up at some point 😉).

Value Types

Value types in Python are those whose variables store the actual value directly. This means that when we assign a variable to another value, a new copy of that value is created in memory.

For example,

# Assigning an integer to a variable
x = 10

# A new copy of the value 10 is created in memory for the variable x
y = x

# Now x and y have independent values in memory

When we modify x or y, each variable has its own space in memory to store its value.

Reference Types

Reference types are those whose variables store a reference (usually the memory address) to the actual object instead of the actual value itself.

This means that when we assign one variable to another, both variables point to the same object in memory.

Let’s see it with an example.

# Assigning a list to a variable
list1 = [1, 2, 3]

# list2 points to the same object in memory as list1
list2 = list1

# Modifying list2 also modifies list1
list2.append(4)
print("list1:", list1)  # Output: [1, 2, 3, 4]

Passing Arguments to Functions

When we pass variables to functions, we need to consider whether they are value types or reference types.

def double_number(num):
    num *= 2
    print("Inside the function:", num)

x = 10
double_number(x)
print("Outside the function:", x)  # x remains 10, it was not modified

def modify_list(lst):
    lst.append("New element")
    print("Inside the function:", lst)

my_list = [1, 2, 3]
modify_list(my_list)
print("Outside the function:", my_list)  # my_list is modified