human
Design and implement a Python program that demonstrates the difference between a class and an object in object-oriented programming languages, while adhering to the following constraints and requirements:

1. Create a class hierarchy consisting of at least three levels of inheritance, with each level having at least two subclasses.

2. Implement encapsulation, by using private attributes and methods, and provide public methods to access and modify them.

3. Implement polymorphism by having at least one method in each class that is overridden in its subclasses. Additionally, implement a method that behaves differently depending on the type of the object it is called on.

4. Utilize a mix of class, static, and instance methods to showcase their differences and use cases.

5. Create instances of different classes and demonstrate how they can interact with each other, either through composition or inheritance.

6. Implement a custom exception class that is thrown and caught in your program to handle any error conditions.

7. Include comments and docstrings to describe the purpose and functionality of each class, method, and module.

8. Provide unit tests with at least 80% code coverage for your implementation.

9. Ensure that your code follows PEP 8 style guidelines and runs without any errors or warnings.
gpt
```python
class CustomException(Exception):
    """Custom exception class for handling specific error conditions."""
    pass


class Animal:
    """Base class for all animals."""

    def __init__(self, name, age):
        self._name = name
        self._age = age

    def get_name(self):
        """Returns the name of the animal."""
        return self._name

    def get_age(self):
        """Returns the age of the animal."""
        return self._age

    def make_sound(self):
        """Returns the sound made by the animal."""
        return "Some generic sound"

    @staticmethod
    def is_animal(obj):
        """Returns True if the object is an instance of Animal, otherwise False."""
        return isinstance(obj, Animal)

    def __str__(self):
        return f"{self.__class__.__name__}({self._name}, {self._age})"


class Mammal(Animal):
    """Base class for mammals."""

    def __init__(self, name, age, has_fur):
        super().__init__(name, age)
        self._has_fur = has_fur

    def has_fur(self):
        """Returns True if the mammal has fur, otherwise False."""
        return self._has_fur


class Reptile(Animal):
    """Base class for reptiles."""

    def __init__(self, name, age, has_scales):
        super().__init__(name, age)
        self._has_scales = has_scales

    def has_scales(self):
        """Returns True if the reptile has scales, otherwise False."""
        return self._has_scales


class Dog(Mammal):
    """Class representing a dog."""

    def __init__(self, name, age, breed):
        super().__init__(name, age, True)
        self._breed = breed

    def get_breed(self):
        """Returns the breed of the dog."""
        return self._breed

    def make_sound(self):
        """Returns the sound made by the dog."""
        return "Woof!"


class Cat(Mammal):
    """Class representing a cat."""

    def __init__(self, name, age, color):
        super().__init__(name, age, True)
        self._color = color

    def get_color(self):
        """Returns the color of the cat."""
        return self._color

    def make_sound(self):
        """Returns the sound made by the cat."""
        return "Meow!"


class Lizard(Reptile):
    """Class representing a lizard."""

    def __init__(self, name, age, length):
        super().__init__(name, age, True)
        self._length = length

    def get_length(self):
        """Returns the length of the lizard."""
        return self._length

    def make_sound(self):
        """Returns the sound made by the lizard."""
        return "Hiss!"


class Snake(Reptile):
    """Class representing a snake."""

    def __init__(self, name, age, venomous):
        super().__init__(name, age, True)
        self._venomous = venomous

    def is_venomous(self):
        """Returns True if the snake is venomous, otherwise False."""
        return self._venomous

    def make_sound(self):
        """Returns the sound made by the snake."""
        return "Sssss!"


def main():
    animals = [
        Dog("Buddy", 3, "Golden Retriever"),
        Cat("Whiskers", 5, "Black"),
        Lizard("Lizzy", 2, 10),
        Snake("Slither", 4, True)
    ]

    for animal in animals:
        if not Animal.is_animal(animal):
            raise CustomException("Not an instance of Animal")

        print(animal)
        print(animal.make_sound())
        print()


if __name__ == "__main__":
    main()
```

To run the unit tests and check the code coverage, you can use the `unittest` and `coverage` modules. First, install the `coverage` module using `pip install coverage`. Then, create a separate file called `test_animals.py` with the following content:

```python
import unittest
from animals import Animal, Mammal, Reptile, Dog, Cat, Lizard, Snake, CustomException


class TestAnimals(unittest.TestCase):

    def test_animal(self):
        animal = Animal("Generic", 1)
        self.assertEqual(animal.get_name(), "Generic")
        self.assertEqual(animal.get_age(), 1)
        self.assertEqual(animal.make_sound(), "Some generic sound")

    def test_mammal(self):
        mammal = Mammal("Mammal", 2, True)
        self.assertEqual(mammal.get_name(), "Mammal")
        self.assertEqual(mammal.get_age(), 2)
        self.assertTrue(mammal.has_fur())

    def test_reptile(self):
        reptile = Reptile("Reptile", 3, True)
        self.assertEqual(reptile.get_name(), "Reptile")
        self.assertEqual(reptile.get_age(), 3)
        self.assertTrue(reptile.has_scales())

    def test_dog(self):
        dog = Dog("Buddy", 3, "Golden Retriever")
        self.assertEqual(dog.get_name(), "Buddy")
        self.assertEqual(dog.get_age(), 3)
        self.assertEqual(dog.get_breed(), "Golden Retriever")
        self.assertEqual(dog.make_sound(), "Woof!")

    def test_cat(self):
        cat = Cat("Whiskers", 5, "Black")
        self.assertEqual(cat.get_name(), "Whiskers")
        self.assertEqual(cat.get_age(), 5)
        self.assertEqual(cat.get_color(), "Black")
        self.assertEqual(cat.make_sound(), "Meow!")

    def test_lizard(self):
        lizard = Lizard("Lizzy", 2, 10)
        self.assertEqual(lizard.get_name(), "Lizzy")
        self.assertEqual(lizard.get_age(), 2)
        self.assertEqual(lizard.get_length(), 10)
        self.assertEqual(lizard.make_sound(), "Hiss!")

    def test_snake(self):
        snake = Snake("Slither", 4, True)
        self.assertEqual(snake.get_name(), "Slither")
        self.assertEqual(snake.get_age(), 4)
        self.assertTrue(snake.is_venomous())
        self.assertEqual(snake.make_sound(), "Sssss!")

    def test_custom_exception(self):
        with self.assertRaises(CustomException):
            raise CustomException("Custom error")


if __name__ == "__main__":
    unittest.main()
```

To run the tests and check the code coverage, run the following commands in the terminal:

```
coverage run test_animals.py
coverage report -m
```

This will show the code coverage for each module and the total coverage percentage.