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AssertionError · Exercises
Core Python

AssertionError Exercises

4 exercises that build on the Python AssertionError lesson, from easy to hard. Each one is checked in your browser when you press Check. Stuck? Use the hint before peeking at the solution.

What this lesson covers: An AssertionError means an assert statement checked a condition that turned out to be False, so something your code assumed to be true was not. By the end you can write assert statements with useful messages, diagnose why one fails, avoid the tuple and float pitfalls, and know when to raise a real exception instead. You will practise: Predict which asserts fail; Make the guard work; Validate with ValueError; Validate input, assert the result.

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1. Predict which asserts fail

Predict the output Easy

Read the code and type exactly what it prints, then press Check.

Read this code 
checks = [(5, "small"), (50, "large"), (500, "huge")]

for value, label in checks:
    try:
        assert value < 100, f"{label} value {value}"
        print("ok", value)
    except AssertionError as err:
        print("failed:", err)




  
  

  
  
  



    
  
    

  

    
2. Make the guard work

    Fix the bug
    Easy
    
  

  
withdraw(balance, amount) should raise an AssertionError with the message "Insufficient funds" when amount is bigger than balance. At the moment the assert never fails. Fix the function.

  
    

  

    Your code
    

      
      
      
      
    

  

  
def withdraw(balance, amount):
    assert (amount <= balance, "Insufficient funds")
    return balance - amount

print(withdraw(100, 30))

  
  
  
  

    
      
      
      
      
    
    
  

  




  
  

  
  
  



    

  
    

  

    
3. Validate with ValueError

    Write code
    Medium
    
  

  
The function check_discount(percent) receives a value typed by a shopper. It should return percent when it is between 0 and 100 (inclusive) and otherwise raise a ValueError (not an AssertionError, because assertions can be switched off).

  
    

  

    Your code
    

      
      
      
      
    

  

  
def check_discount(percent):
    assert 0 <= percent <= 100
    return percent


  
  
  
  

    
      
      
      
      
    
    
  

  




  
  

  
  
  



    
  
    

  

    
4. Validate input, assert the result

    Write code
    Hard
    
  

  
Write normalize(weights) that returns a list where each weight is divided by the sum, so the results add up to 1. Raise ValueError if the list is empty or the sum is not positive (that is bad input). After computing the result, use an assert with math.isclose to check your own invariant that the new list sums to 1.

  
    

  

    Your code
    

      
      
      
      
    

  

  
import math

def normalize(weights):
    pass


  
  
  
  

    
      
      
      
      
    
    
  

  




  
  

  
  
  



    
  
  

    Next lessonPython StopIteration
    
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