What is pass statement in Python?

The pass statement is often used in places where code is syntactically required, but we don’t want to write any implementation yet.

The pass statement is a placeholder in Python, used when a statement is syntactically required but no action is needed. It’s a simple way to tell the interpreter, “I know this is a part of my code, but I'll fill it in later.” In short, the pass statement allows us to complete our code later without causing errors in the meantime.

Syntax of the pass statement

The pass statement in Python is simple and intuitive. Its syntax is:

pass
pass statement syntax

Why and when to use Python pass statements

Imagine you’re designing a to-do list manager in Python. You plan to implement several features, but you want to lay out the basic structure first. There are some features you haven’t decided how to implement yet, and you want the code to run without errors as you continue working on it. For example, in function definitions, loops, or conditionals that you might plan to complete later.

This is where the pass statement shines. It lets you define placeholders for future code while keeping your project error-free and running smoothly.

Maintaining code structure with pass

It can be used in function definitions, loops, and conditional statements when you want to outline your code but aren’t ready to fill in all the logic. It allows the code to remain valid and runnable, making it easier to iterate on larger projects.

Avoiding errors with pass
Without the pass statement, Python would raise an IndentationError if we leave a class, function, loop, or conditional block empty. The pass keyword ensures that our code remains valid while we develop the rest of our program.

Debugging or stubbing code

When refactoring or debugging code, you might temporarily replace parts of the logic with pass to isolate other parts of the system. This allows you to comment out large sections of the program or “stub out” functionality without deleting the code.

Examples of using pass statements in different contexts

Let’s take our to-do list manager example for this. We know we need a class TodoManager to handle all tasks, but we haven’t decided how each feature will be implemented.

Using the pass statement in a class definition

We have a class structure below. 

class TodoManager:
  pass

That's it! Running the code above above gives no error. In this case, pass tells Python to skip that block, making the syntax valid. Go ahead and remove even a single pass statement in the code above, it would give an IndentationError.

Using the pass statement in a function(s)

Similarly, suppose we want our to-do list manager to have these features:

  1. Adding a task

  2. Marking a task as completed

  3. Removing a task

  4. Displaying tasks

We can structure this in Python using functions, but we’ll leave their implementation to be completed later using pass.

class TodoManager:
  def __init__(self):
    pass  # We'll add initialization code later
  def add_task(self, task):
    pass  # Implementation for adding task will come later
  def mark_task_completed(self, task):
    pass  # This will mark a task as completed
  
  def remove_task(self, task):
      pass  # Removing a task logic will come here
    
  def display_tasks(self):
    pass  # Code for showing all tasks will be added later

Here, pass allows us to define the overall structure of the class and the methods, even if we haven’t implemented the functionality yet. This helps us see the bigger picture without worrying about the details for now.

Using the pass statement in an empty loop or condition

Let’s say we plan to loop through the tasks to display them later, but for now, we just want to test the structure:

def display_tasks(self):
    for task in []:  # Assume tasks will be stored in a list later
        pass  # I'll add the code to display tasks later

Inside a conditional statement

We can also use pass as a placeholder inside conditional statements.

def display_tasks(self):
  for task in []:  # Placeholder for tasks
    if True:  # Placeholder condition
        pass  # Add logic to show tasks later
    else:
        print(task)

Let’s look at a different example of using pass in conditional statements:

# This functions prints the number if its not 2
def display(number):
  
  if number is 2:
    pass # Pass statement
  else:
    print ("Number: ", number)
    
display(2)
display(3)

Here, if has no implementation and the code still works.

Feel free to remove/move/swap the pass statement in the code above and observe the difference it makes.

Code execution with the pass statement

Let’s see the illustration below to understand how the code execution with pass statement works:

Code execution with the pass statement
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Exercise: Build a simple number guessing game

As a fun exercise, create a simple number-guessing game where the player has to guess a randomly chosen number. During the development process, you will use pass statements to stub out parts of the game that you have not yet implemented.

Instructions

  1. Setup the game: Your program should randomly choose a number between 1 and 10.

  2. Generate guesses: The program will automatically generate guesses.

  3. Check the guess: If the generated guess is correct, the program should display a congratulatory message. If it’s incorrect, it should indicate whether the guess was too low or too high.

  4. Use pass statements: Use pass in sections where you plan to implement future features, such as limiting the number of guesses or providing hints.

  5. Future improvements: After completing the basic structure, think of at least one additional feature you could add, like:

    1. Think about how you might improve the hint system for future implementation. For example, you could track previous guesses and provide feedback.

    2. Consider how you might limit the number of guesses or implement a scoring system.

    3. Test the game by running your code and observing the output.

    4. The program should automatically generate guesses and check them against the secret number.

import random
def guessing_game():
  secret_number = random.randint(1, 10)  # Randomly chosen number
  guesses = 0  # Counter for the number of guesses
  print("Welcome to the Number Guessing Game!")
  print("I have selected a number between 1 and 10. Let's see if I can guess it!")
  
  # Add your code here.
# Start the game
guessing_game()

If you are stuck, refer to the "Solution" after pressing the "Run" button for guidance.

Key takeaways

  • Placeholder for future code: The pass statement acts as a placeholder in blocks of code (functions, classes, loops, or conditionals) where no action is required yet, allowing you to define the structure without causing syntax errors.

  • Keeps code clean and organized: It helps maintain a clean and structured codebase during the development process, letting you outline logic without needing to implement details right away.

  • Prevents errors in empty blocks: By using pass, you can avoid errors that arise when Python encounters empty blocks of code, ensuring your code runs smoothly.

  • Commonly used in stubs: It is particularly useful when building stubs or prototypes, where parts of the code will be implemented later.

  • Non-operational: The pass statement performs no operation and is effectively a “do nothing” statement.

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Frequently asked questions

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What's the difference between pass, return, and break in Python?

  • pass: This does nothing and is used as a placeholder.
  • return: This exits a function and optionally returns a value.
  • break: This exits a loop prematurely. Each of these serves a different control flow purpose in Python, and they are not interchangeable.

Example of each:

for i in range(5):
    if i == 2:
        pass  # Do nothing, just continue the loop
    elif i == 3:
        break  # Exit the loop
    else:
        print(i)

def my_function():
    return  # Exit the function

Have a look at “What are break, continue, and pass statements in Python?” for an interesting discussion on this topic.

How is a pass statement different from a comment in Python?

The pass statement and comments serve different purposes. Comments (using #) are ignored by Python during execution and are used for documentation purposes, whereas the pass statement is an actual statement that tells Python to do nothing but keeps the structure of the code valid. It can be used inside functions, loops, and classes, where a statement is required.

Why do I get an IndentationError when I leave a class, function, or loop empty?

In Python, leaving blocks such as classes, functions, loops, or conditionals empty will result in an IndentationError because Python expects every indented block to contain code. You can avoid this error by using the pass statement as a placeholder.

Can I use the pass statement in a Python try-except block?

Yes, you can use the pass statement in a try-except block when you want to catch an exception but don’t want to take any specific action immediately. This is useful when you need to handle exceptions temporarily or when you plan to handle them later.

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