Assert statement usage in Python - Mini Project: Build & Apply

Assert Statement Usage

📖 Scenario: You are working on a simple program that checks if a user's age is valid for a certain activity. You want to make sure the age is not negative and is within a reasonable range.

🎯 Goal: Build a program that uses assert statements to check the validity of an age value.

📋 What You'll Learn

Create a variable called age with a specific integer value.

Create a variable called max_age to set the maximum allowed age.

Use assert statements to check that age is not negative and does not exceed max_age.

Print a message confirming the age is valid.

💡 Why This Matters

🌍 Real World

Assert statements help programmers catch mistakes early by checking if values are correct while the program runs.

💼 Career

Many software jobs require writing code that safely checks data and assumptions to avoid bugs and errors.

1

Create the age variable

Create a variable called age and set it to the integer value 25.

Python

# Create a variable called age and set it to 25
# Your code here

Hint

Use a simple assignment like age = 25.

2

Create the max_age variable

Create a variable called max_age and set it to the integer value 120.

Python

age = 25
# Create a variable called max_age and set it to 120
# Your code here

Hint

Use a simple assignment like max_age = 120.

3

Add assert statements to check age

Add two assert statements: one to check that age is greater than or equal to 0, and another to check that age is less than or equal to max_age.

Python

age = 25
max_age = 120
# Add assert statements to check age is >= 0 and <= max_age
# Your code here

Hint

Use assert age >= 0 and assert age <= max_age.

4

Print confirmation message

Write a print statement that outputs the exact text: "Age is valid."

Python

age = 25
max_age = 120
assert age >= 0
assert age <= max_age
# Print "Age is valid." below
# Your code here

Hint

Use print("Age is valid.") to show the message.

Practice

1. What does the assert statement do in Python?

easy

A. Prints a message when a condition is false

B. Runs a loop until a condition is true

C. Defines a function to check conditions

D. Checks if a condition is true and stops the program if false

Solution

1. Step 1: Understand the purpose of assert

   The assert statement tests a condition and raises an error if the condition is false.

2. Step 2: Compare options with assert behavior

   Only Checks if a condition is true and stops the program if false correctly describes assert's behavior of stopping the program when the condition is false.

3. Final Answer:

   Checks if a condition is true and stops the program if false -> Option D

4. Quick Check:

   Assert checks condition and stops if false [OK]

Hint: Assert stops program if condition is false [OK]

Common Mistakes:

• Thinking assert runs loops
• Confusing assert with print
• Believing assert defines functions

2. Which of the following is the correct syntax for an assert statement with a message?

easy

A. assert x > 0, "x must be positive"

B. assert (x > 0) "x must be positive"

C. assert x > 0; "x must be positive"

D. assert x > 0: "x must be positive"

Solution

1. Step 1: Recall assert syntax

   The correct syntax is assert condition, message with a comma separating condition and message.

2. Step 2: Check each option

   Only assert x > 0, "x must be positive" uses a comma correctly between condition and message.

3. Final Answer:

   assert x > 0, "x must be positive" -> Option A

4. Quick Check:

   Assert syntax uses comma before message [OK]

Hint: Use comma between condition and message in assert [OK]

Common Mistakes:

• Using colon or semicolon instead of comma
• Missing comma before message
• Putting message without quotes

3. What will be the output of this code?

def check_age(age):
    assert age >= 18, "Age must be at least 18"
    return "Access granted"

print(check_age(20))
print(check_age(16))

medium

A. Access granted\nAccess granted

B. Access granted\nAssertionError: Age must be at least 18

C. AssertionError: Age must be at least 18\nAccess granted

D. No output, program crashes immediately

Solution

1. Step 1: Analyze first function call

   check_age(20) passes the assert since 20 >= 18, so it returns "Access granted" and prints it.

2. Step 2: Analyze second function call

   check_age(16) fails the assert because 16 < 18, so it raises AssertionError with the message.

3. Final Answer:

   Access granted\nAssertionError: Age must be at least 18 -> Option B

4. Quick Check:

   Assert stops program on false condition with error [OK]

Hint: Assert stops at first false condition with error [OK]

Common Mistakes:

• Thinking both print statements run
• Ignoring the error message
• Assuming assert prints message without error

4. Find the error in this code snippet:

assert x > 10 "x should be greater than 10"

medium

A. Missing comma between condition and message

B. Missing parentheses around condition

C. Message should be a variable, not a string

D. Assert cannot have a message

Solution

1. Step 1: Check assert syntax

   Assert requires a comma between the condition and the message string.

2. Step 2: Identify the error

   The code misses the comma, causing a syntax error.

3. Final Answer:

   Missing comma between condition and message -> Option A

4. Quick Check:

   Comma separates condition and message in assert [OK]

Hint: Always put a comma before the assert message [OK]

Common Mistakes:

• Using colon or space instead of comma
• Thinking parentheses are mandatory
• Believing assert can't have messages

5. You want to check a list of numbers to ensure all are positive using assert. Which code correctly uses assert inside a loop to do this?

nums = [3, 5, -1, 7]
for n in nums:
    ?

hard

A. assert n > 0; f"Number {n} is not positive"

B. assert n > 0: f"Number {n} is not positive"

C. assert n > 0, f"Number {n} is not positive"

D. assert (n > 0), "Number n is not positive"

Solution

1. Step 1: Understand assert in loop context

   We want to check each number and stop if any is not positive, showing which one failed.

2. Step 2: Check syntax correctness

   assert n > 0, f"Number {n} is not positive" uses correct assert syntax with a comma and f-string for message. Others use invalid punctuation.

3. Final Answer:

   assert n > 0, f"Number {n} is not positive" -> Option C

4. Quick Check:

   Assert syntax: condition, message with comma [OK]

Hint: Use comma and f-string for assert message in loops [OK]

Common Mistakes:

• Using colon or semicolon instead of comma
• Not using f-string for variable message
• Putting message outside assert statement