Rectangle.py

class Rectangle:
    def __init__(self, length, width):
        self._length = length
        self._width = width
        # Check the invariant after initializing the attributes
        self._check_invariant()

    def _check_invariant(self):
        # Invariant: Both length and width must be positive
        if self._length <= 0 or self._width <= 0:
            raise ValueError("Invariant violation: Length and width must be positive.")

    @property
    def length(self):
        return self._length

    @length.setter
    def length(self, value):
        self._length = value
        # Check the invariant after modifying the attribute
        self._check_invariant()

    @property
    def width(self):
        return self._width

    @width.setter
    def width(self, value):
        self._width = value
        # Check the invariant after modifying the attribute
        self._check_invariant()

# Example usage:
try:
    # Creating a rectangle with invalid dimensions
    invalid_rectangle = Rectangle(-2, 5)
except ValueError as e:
    print(e)

# Creating a valid rectangle
valid_rectangle = Rectangle(4, 3)
print("Length:", valid_rectangle.length)
print("Width:", valid_rectangle.width)

# Modifying attributes and maintaining the invariant
valid_rectangle.length = 7
valid_rectangle.width = 2
print("Modified Length:", valid_rectangle.length)
print("Modified Width:", valid_rectangle.width)