how to use assert in python function?

In Python, assert is used as a debugging aid that tests a condition. If the condition is True, the program continues to execute. If the condition is False, an AssertionError is raised with an optional message. This is often used to check if certain conditions hold true, especially during development or testing.

Here's how you can use assert in a Python function:

Example 1: Basic Usage

def divide(a, b):
    assert b != 0, "The divisor (b) cannot be zero"
    return a / b

result = divide(10, 2)  # This will work fine
print(result)

result = divide(10, 0)  # This will raise an AssertionError with the message "The divisor (b) cannot be zero"

Example 2: Asserting Multiple Conditions

You can use assert to check multiple conditions within a function.

Example 3: Using assert with Functions Returning Values

In this example, we use assert to check the output of a function to ensure it meets certain criteria

def get_age(birth_year, current_year):
    age = current_year - birth_year
    assert age >= 0, "Age cannot be negative"
    return age

print(get_age(2000, 2024))  # This will work fine and return 24

print(get_age(2024, 2000))  # This will raise an AssertionError with the message "Age cannot be negative"

Example 4: Using assert to Validate Input Arguments

Here, assert is used to validate the inputs to a function to ensure they meet expected conditions.

def calculate_discount(price, discount):
    assert price > 0, "Price must be greater than zero"
    assert 0 <= discount <= 100, "Discount must be between 0 and 100"
    
    discounted_price = price - (price * discount / 100)
    return discounted_price

print(calculate_discount(100, 20))  # This will work fine and return 80.0

print(calculate_discount(-100, 20))  # This will raise an AssertionError with the message "Price must be greater than zero"

Example 5: Using assert in a Loop

You can also use assert within loops to check conditions as the loop iterates.

def find_first_even(numbers):
    for number in numbers:
        assert isinstance(number, int), f"All elements must be integers, but found {type(number)}"
        if number % 2 == 0:
            return number
    return None

print(find_first_even([1, 3, 7, 10, 13]))  # This will return 10

print(find_first_even([1, 3, '7', 10, 13]))  # This will raise an AssertionError with the message "All elements must be integers, but found <class 'str'>"

Example 6: Disabling Assertions in Production

By default, assertions are enabled, but you can disable them in production by running Python with the -O (optimize) flag. This will skip any assert statements

python -O your_script.py

Key Points:

  1. Condition: The expression after assert is evaluated. If it’s True, the program continues to execute; if False, an AssertionError is raised.
  2. Optional Message: You can provide an optional message to be displayed when the assertion fails, which can help in debugging.
  3. Usage: Assertions are generally used during development and testing, not in production code. For production, you might want to use error handling mechanisms like try-except.

Summary:

  • assert is a powerful tool for validating conditions during development and testing.
  • It helps catch bugs early by ensuring certain conditions hold true at runtime.
  • In production, assertions can be disabled, so they should not be used for critical checks.

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