Understand the Key Difference Between Function and Method in Python!

Functions and methods are fundamental concepts in Python programming. A function is a standalone block of code designed to perform a specific task, while a method is a function that is associated with an object or class. Understanding the difference between function and method in Python is essential for writing clean and efficient code. 

In this guide, you'll read more about defining functions and methods, the Difference Between Function and Method in Python. We'll also cover practical use cases, and best practices for choosing between functions and methods in your Python programs.

Function vs. Method: A Head-to-Head Comparison 

Let's get straight to the point. The best way to understand the difference between function and method in Python is to see them compared side-by-side. While both are reusable blocks of code, their relationship with objects and how they are called are fundamentally different. 

This table provides a comprehensive overview of their core distinctions. 

This table captures the essential difference between method and function in python. Now, let's take a closer look at each of them to understand the concepts more deeply. 

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A Deeper Look at Functions in Python 

A function is the most basic unit of reusable code in Python. It's a self-contained block that you can define once and run many times. The key takeaway is that functions are independent. They don't need the context of a class or an object to operate. 

The Anatomy of a Function 

A function is defined using the def keyword. Its structure includes: 

1. The def keyword: Signals the start of a function definition. 
2. A function name: A unique name to identify and call the function. 
3. Parameters (optional): Variables listed inside the parentheses () that the function can accept as input. 
4. A colon :: Marks the end of the function header. 
5. An indented code block: The lines of code that the function will execute. 
6. A return statement (optional): Sends a value back from the function. 

A Clear Example 

Let's look at a simple, standalone function that greets a user. 

Python 
# Defining a standalone function 
def greet_user(name): 
  """This function takes a name and prints a greeting.""" 
  message = f"Hello, {name}! Welcome." 
  print(message) 
 
# Calling the function directly by its name 
greet_user("Alex") 
greet_user("Brenda") 
 

Output: 

Hello, Alex! Welcome. 
Hello, Brenda! Welcome. 
 

As you can see, greet_user exists on its own. We call it directly and give it the data it needs to work ("Alex"). It doesn't know about any objects or classes; it just performs its task and finishes. This independence is the hallmark of a function. 

Also Read: How to Call a Function in Python? 

A Deeper Look at Methods in Python 

A method shares the same DNA as a function—it's a block of code defined with def—but it lives inside a class. This placement fundamentally changes its behavior. A method is intrinsically linked to an object (an instance of the class) and is designed to work with that object's data. 

The Role of self 

The most distinct feature of a method is its first parameter, self. When you call a method on an object, like my_object.do_something(), Python automatically passes my_object as the first argument to the method. The self parameter is there to receive this object. This gives the method the ability to read and change the object's attributes. 

A Clear Example 

Let's create a BankAccount class. The actions you can perform—depositing, withdrawing—are perfect candidates for methods because they need to modify the account's balance. 

Python 

# Defining a class 
class BankAccount: 
  def __init__(self, owner, balance=0): 
    self.owner = owner 
    self.balance = balance 
 
  # A method to deposit money 
  def deposit(self, amount): 
    self.balance += amount 
    print(f"Added {amount}. New balance is {self.balance}.") 
 
  # A method to withdraw money 
  def withdraw(self, amount): 
    if amount > self.balance: 
      print("Insufficient funds!") 
    else: 
      self.balance -= amount 
      print(f"Withdrew {amount}. New balance is {self.balance}.") 
 
# Create an instance (object) of the class 
my_account = BankAccount("John Doe", 1000) 
 
# Call methods ON the object 
my_account.deposit(500) 
my_account.withdraw(200) 
 

Output: 

Added 500. New balance is 1500. 
Withdrew 200. New balance is 1300. 
 

Here, deposit and withdraw are methods. They use self to access and modify self.balance, the internal data of the my_account object. This ability to manage an object's state is the primary purpose of a method and a key difference between method and function in python. 

Also Read: Understanding List Methods in Python with Examples 

Real-World Examples: Functions and Methods in Action 

The distinction between functions and methods becomes even clearer when you look at Python's built-in tools. 

Built-in Functions You Use Every Day 

Python provides many functions that are globally available. They are classic examples of standalone, independent functions. 

• len(): A universal function to get the length of an object. 
• print(): A function to display output to the console. 
• sum(): A function to sum the items of an iterable. 

Python 
my_items = [10, 20, 30] 
my_message = "Python" 
 
# Calling built-in functions 
print(f"The number of items is: {len(my_items)}") 
print(f"The sum of items is: {sum(my_items)}") 
print(f"The length of the message is: {len(my_message)}") 
 

Notice that we pass the object (e.g., my_items) into the function. 

Built-in Methods on Common Objects 

Common data types like strings and lists are objects, and they come with a rich set of methods you can use. 

• String methods: .upper(), .replace(), .strip() 
• List methods: .append(), .sort(), .pop() 

Python 
my_items = [4, 2, 8] 
my_message = "  hello world  " 
 
# Calling methods on a list object 
my_items.append(1) 
my_items.sort() 
print(f"Modified list: {my_items}") 
 
# Calling methods on a string object 
cleaned_message = my_message.strip() 
uppercase_message = cleaned_message.upper() 
print(f"Modified message: {uppercase_message}") 
 

Output: 

Modified list: [1, 2, 4, 8] 
Modified message: HELLO WORLD 
 

Here, we call the method on the object (my_items.sort()). This is the most visible difference between function and method in Python in day-to-day coding. 

Also Read: Module and Package in Python 

Conclusion 

While they are both callable blocks of code, the difference between function and method in Python is a cornerstone of object-oriented programming. The simplest way to remember it is: a method is a function that is bound to an object, while a function is independent. 

This distinction appears in how they are called (dot notation for methods) and in the special self parameter that gives methods their power to manage an object's state. Understanding when to use a standalone function versus a class method is a sign of a maturing Python developer. Grasping this concept is a major milestone on your journey to writing clean, organized, and powerful object-oriented code. 

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