Magic Methods Practice Exercises¶

Exercise 1: Temperature Class¶

Create a Temperature class that: - Stores temperature in Celsius - Implements __init__, __repr__, and __str__ - Implements comparison operators (__eq__, __lt__, __gt__, etc.) - Implements arithmetic operators to add/subtract temperatures - Has a custom __format__ method that supports 'C', 'F', and 'K' format specs

Example usage:

t1 = Temperature(25)
t2 = Temperature(30)
print(t1)  # "25.0°C"
print(f"{t1:F}")  # "77.0°F"
print(t1 < t2)  # True
print(t1 + 5)  # Temperature(30)

Exercise 2: Shopping Cart¶

Create a ShoppingCart class that: - Implements __len__ to return the number of items - Implements __getitem__ to access items by index - Implements __setitem__ to update items - Implements __delitem__ to remove items - Implements __contains__ to check if an item is in the cart - Implements __iter__ to iterate over items - Has an add_item(item, quantity, price) method - Has a total() method that returns the total cost

Exercise 3: Fraction Class¶

Create a Fraction class that: - Stores numerator and denominator - Implements all arithmetic operators (__add__, __sub__, __mul__, __truediv__) - Automatically simplifies fractions (greatest common divisor) - Implements comparison operators - Implements __str__ to display as "numerator/denominator" - Implements __float__ to convert to decimal - Handles division by zero appropriately

Example usage:

f1 = Fraction(1, 2)
f2 = Fraction(1, 3)
print(f1 + f2)  # 5/6
print(f1 * f2)  # 1/6
print(float(f1))  # 0.5

Exercise 4: Range-like Class¶

Create a CustomRange class that mimics Python's built-in range(): - Implements __init__ with start, stop, and step parameters - Implements __len__ to return the number of elements - Implements __getitem__ to access elements by index - Implements __contains__ to check if a value is in the range - Implements __iter__ to make it iterable - Implements __reversed__ for reverse iteration

Exercise 5: Callable Validator¶

Create a Validator class that: - Takes validation rules in __init__ (e.g., min, max, type) - Implements __call__ to validate a value - Returns True if valid, False otherwise - Can be used as a decorator for functions

Example usage:

age_validator = Validator(min=0, max=150, type=int)
print(age_validator(25))  # True
print(age_validator(-5))  # False

Exercise 6: File Logger Context Manager¶

Create a FileLogger context manager that: - Opens a log file when entering the context - Implements __enter__ and __exit__ - Provides a log(message) method - Automatically adds timestamps to log entries - Safely closes the file even if exceptions occur - Optionally formats exceptions in the log

Example usage:

with FileLogger('app.log') as logger:
    logger.log('Application started')
    # do some work
    logger.log('Processing complete')

Exercise 7: Coordinate System¶

Create a Coordinate class that: - Represents a point in 2D space - Implements arithmetic operators for vector operations - Implements __abs__ to return distance from origin - Implements __eq__ and __hash__ so coordinates can be used in sets - Implements __neg__ to reflect across origin - Has a distance_to(other) method

Exercise 8: Counter Dictionary¶

Create a CounterDict class that: - Automatically initializes missing keys to 0 - Implements __missing__ for default values - Implements __getitem__ and __setitem__ - Implements arithmetic operators to combine counters - Has a most_common(n) method

Example usage:

counter = CounterDict()
counter['a'] = 5
counter['b'] = 3
print(counter['c'])  # 0 (not KeyError)

Exercise 9: Smart String¶

Create a SmartString class that: - Wraps a regular string - Implements __len__, __getitem__, and __iter__ - Implements __add__ for concatenation - Implements __mul__ for repetition - Implements __contains__ for substring checking - Implements comparison operators (case-insensitive) - Implements __int__ and __float__ for conversion (if possible)

Exercise 10: Matrix Operations¶

Create a Matrix class that: - Stores a 2D grid of numbers - Implements __add__ and __sub__ for matrix addition/subtraction - Implements __mul__ for scalar multiplication and matrix multiplication - Implements __getitem__ with tuple indexing (row, col) - Implements __eq__ for matrix equality - Has methods for transpose(), determinant() (for 2x2)

Challenge Exercise: Database-like Table¶

Create a Table class that: - Stores rows of data with named columns - Implements __len__ for number of rows - Implements __getitem__ to get rows by index or columns by name - Implements __iter__ to iterate over rows - Implements __contains__ to check if a value exists in any column - Has methods: add_row(), filter(), sort_by(column), select(columns) - Can be used as a context manager to auto-save to file

This is a complex exercise that combines multiple magic methods!

Testing Your Solutions¶

For each exercise, write test cases that verify: 1. All magic methods work correctly 2. Edge cases are handled (empty inputs, None, zeros, etc.) 3. Type checking works appropriately 4. Error messages are clear and helpful

Good luck! 🚀