Polymorphism through functions in Python - Mini Project: Build & Apply

Polymorphism through functions

📖 Scenario: Imagine you are creating a simple program that can greet different types of people or animals. Each type has its own way of greeting, but you want to use the same function name to say hello. This is called polymorphism, where one function name works differently depending on the input.

🎯 Goal: You will build a program that defines different greeting functions for a Person and a Dog. Then you will write a single function called greet that calls the correct greeting based on the input. Finally, you will test the greet function with both a person and a dog.

📋 What You'll Learn

Create two classes: Person and Dog with their own greeting methods

Create a function called greet that takes one argument and calls the correct greeting method

Test the greet function with a Person instance and a Dog instance

Print the greetings to see the different outputs

💡 Why This Matters

🌍 Real World

Polymorphism helps programmers write flexible code that can work with different types of objects without changing the function names. For example, a messaging app might use polymorphism to send messages to different devices like phones, tablets, or computers using the same function name.

💼 Career

Understanding polymorphism is important for software developers because it allows writing cleaner, reusable, and easier-to-maintain code. It is a key concept in object-oriented programming used in many programming jobs.

1

Create Person and Dog classes with greeting methods

Create a class called Person with a method say_hello that returns the string "Hello, I am a person.". Also create a class called Dog with a method say_hello that returns the string "Woof! I am a dog.".

Python

# Your code here

Hint

Remember to use def say_hello(self): inside each class and return the exact greeting strings.

2

Create the greet function

Create a function called greet that takes one parameter called entity. Inside the function, call the say_hello method of entity and return its result.

Python

class Person:
    def say_hello(self):
        return "Hello, I am a person."

class Dog:
    def say_hello(self):
        return "Woof! I am a dog."

# Your code here

Hint

Use entity.say_hello() to call the method on the passed object.

3

Create instances of Person and Dog

Create a variable called person and assign it an instance of the Person class. Create another variable called dog and assign it an instance of the Dog class.

Python

class Person:
    def say_hello(self):
        return "Hello, I am a person."

class Dog:
    def say_hello(self):
        return "Woof! I am a dog."

def greet(entity):
    return entity.say_hello()

# Your code here

Hint

Use person = Person() and dog = Dog() to create the objects.

4

Print greetings using the greet function

Use the print function to display the result of calling greet(person) and then greet(dog).

Python

class Person:
    def say_hello(self):
        return "Hello, I am a person."

class Dog:
    def say_hello(self):
        return "Woof! I am a dog."

def greet(entity):
    return entity.say_hello()

person = Person()
dog = Dog()

# Your code here

Hint

Use print(greet(person)) and print(greet(dog)) to show the greetings.

Practice

1.

What does polymorphism through functions mean in Python?

easy

A. Functions cannot be reused with different inputs

B. Multiple functions have the same name but different parameters

C. Functions can only accept one specific data type

D. A single function works with different data types

Solution

1. Step 1: Understand polymorphism concept

   Polymorphism means one function can handle different types of inputs.

2. Step 2: Relate to function behavior

   In Python, a single function can accept various data types and behave accordingly.

3. Final Answer:

   A single function works with different data types -> Option D

4. Quick Check:

   Polymorphism = single function, many types [OK]

Hint: Think: one function, many input types [OK]

Common Mistakes:

• Confusing polymorphism with function overloading
• Believing functions accept only one data type
• Mixing polymorphism with inheritance

2.

Which of the following is the correct way to check a variable's type inside a function for polymorphism?

def process(value):
    # What to use here?
    pass

easy

A. if type(value) == int:

B. if value is int:

C. if isinstance(value, int):

D. if value == int:

Solution

1. Step 1: Recall Python type checking methods

   Using isinstance() is the recommended way to check type in Python.

2. Step 2: Compare options

   if isinstance(value, int): uses isinstance(value, int), which correctly checks if value is an int or subclass.

3. Final Answer:

   if isinstance(value, int): -> Option C

4. Quick Check:

   Use isinstance() for type checks [OK]

Hint: Use isinstance() to check types safely [OK]

Common Mistakes:

• Using 'type() == int' which fails with subclasses
• Using 'is' or '==' incorrectly for type comparison
• Not checking type at all

3.

What is the output of this code?

def describe(value):
    if isinstance(value, int):
        return f"Integer: {value}"
    elif isinstance(value, str):
        return f"String: {value}"
    else:
        return "Unknown type"

print(describe(10))
print(describe('hello'))
print(describe(3.14))

medium

A. Integer: 10\nString: hello\nUnknown type

B. Integer: 10\nString: hello\nFloat: 3.14

C. Unknown type\nUnknown type\nUnknown type

D. Integer: 10\nUnknown type\nUnknown type

Solution

1. Step 1: Check input 10

   10 is int, so returns 'Integer: 10'.

2. Step 2: Check input 'hello'

   'hello' is str, so returns 'String: hello'.

3. Step 3: Check input 3.14

   3.14 is float, not int or str, so returns 'Unknown type'.

4. Final Answer:

   Integer: 10 String: hello Unknown type -> Option A

5. Quick Check:

   Type checks match outputs [OK]

Hint: Match isinstance checks to output lines [OK]

Common Mistakes:

• Assuming float is handled like int or str
• Ignoring else case output
• Mixing output order

4.

Find the error in this polymorphic function and fix it:

def process(value):
    if isinstance(value, int):
        return value * 2
    elif isinstance(value, str):
        return value + value
    else:
        return value / 2

print(process('abc'))
print(process([1, 2, 3]))

medium

A. No error; code runs fine

B. Error: Cannot divide list by 2; fix by handling list separately

C. Error: Missing return statement for int type

D. Error: Cannot multiply string by 2; fix by converting to int

Solution

1. Step 1: Analyze input 'abc'

   String input returns 'abcabc' by concatenation, no error.

2. Step 2: Analyze input [1, 2, 3]

   List input goes to else: value / 2, but dividing list by 2 causes TypeError.

3. Step 3: Fix the error

   Need to add a check for list type or avoid dividing list by 2.

4. Final Answer:

   Error: Cannot divide list by 2; fix by handling list separately -> Option B

5. Quick Check:

   List / 2 causes error [OK]

Hint: Check operations valid for each type [OK]

Common Mistakes:

• Assuming all types support division
• Not testing with different input types
• Ignoring TypeError exceptions

5.

Write a polymorphic function combine that accepts either two strings or two lists and returns their concatenation. What is the output of this code?

def combine(a, b):
    if isinstance(a, str) and isinstance(b, str):
        return a + b
    elif isinstance(a, list) and isinstance(b, list):
        return a + b
    else:
        return None

print(combine('Hi, ', 'there!'))
print(combine([1, 2], [3, 4]))
print(combine('Hello', [1, 2]))

hard

A. 'Hi, there!'\n[1, 2, 3, 4]\nNone

B. 'Hi, there!'\n[1, 2]\n[3, 4]

C. None\nNone\nNone

D. 'Hi, there!'\nNone\nNone

Solution

1. Step 1: Check first call combine('Hi, ', 'there!')

   Both are strings, so returns concatenation 'Hi, there!'.

2. Step 2: Check second call combine([1, 2], [3, 4])

   Both are lists, so returns concatenated list [1, 2, 3, 4].

3. Step 3: Check third call combine('Hello', [1, 2])

   Types differ, so returns None.

4. Final Answer:

   'Hi, there!' [1, 2, 3, 4] None -> Option A

5. Quick Check:

   Type checks control output [OK]

Hint: Check types of both inputs before combining [OK]

Common Mistakes:

• Not checking both inputs' types
• Trying to combine different types directly
• Returning wrong default for mismatched types