Everything is an Object in Python

Introduction

In Python, everything is an object. At first, this sounded abstract to me, but after going through this project, it makes a lot more sense. Whether it’s a number, a list, a string, or even a function, they all behave as objects. This affects how Python stores data, manages memory, and handles variables.

id and type

Every object in Python has a unique identity and a type. The id() function gives you the memory address (in CPython) and type() tells you what kind of object it is. Two objects can have the same value but different ids.

a = 5
b = 5
print(id(a) == id(b))  # True (because Python reuses small integers)

x = [1, 2]
y = [1, 2]
print(id(x) == id(y))  # False

Mutable Objects

Mutable means the object can change. Lists, dictionaries, and sets are mutable. If you pass a list to a function and change it, the original list changes too.

my_list = [1, 2]
my_list.append(3)
print(my_list)  # [1, 2, 3]

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Immutable Objects

Immutable objects cannot change after creation. Numbers, strings, and tuples are immutable. If you “change” them, Python creates a new object.

a = "Hello"
a += " World"
print(a)  # "Hello World"

Even though it looks like the original string changed, it didn’t — a new string was created.

Why it matters

It matters because it can lead to bugs if you don’t understand how Python handles these objects. For example, using += on a list changes it in-place, but using + creates a new object.

a = [1, 2]
b = a
a += [3]
print(b)  # [1, 2, 3]

a = [1, 2]
b = a
a = a + [3]
print(b)  # [1, 2]

Function arguments

When passing arguments to functions, Python sends a reference to the object. If it’s mutable, changes inside the function will affect the original. If it’s immutable, it won’t.

def change_val(n):
    n += 1

a = 10
change_val(a)
print(a)  # 10

def modify_list(lst):
    lst.append(100)

my_list = [1, 2]
modify_list(my_list)
print(my_list)  # [1, 2, 100]

Conclusion

This project helped me better understand how Python deals with objects. Knowing the difference between mutable and immutable types, and how Python passes variables to functions, makes a big difference when writing code that behaves the way I expect.