Functions and Object-Oriented Programming (OOP) are key concepts in Python that help organize and structure code efficiently. Understanding these concepts will improve code reusability, maintainability, and readability.
In this post, we’ll cover:
Functions in Python – Defining, calling, and using arguments
Lambda functions – Writing concise, one-liner functions
Object-Oriented Programming (OOP) – Classes, objects, inheritance, and encapsulation
Let’s get started!
1️⃣ Functions in Python
What is a Function?
A function is a block of reusable code that performs a specific task.
Defining and Calling Functions
<span>def</span> <span>greet</span><span>(</span><span>name</span><span>):</span> <span># Function definition </span> <span>return</span> <span>f</span><span>"</span><span>Hello, </span><span>{</span><span>name</span><span>}</span><span>!</span><span>"</span><span>print</span><span>(</span><span>greet</span><span>(</span><span>"</span><span>Alice</span><span>"</span><span>))</span> <span># Calling the function </span><span>def</span> <span>greet</span><span>(</span><span>name</span><span>):</span> <span># Function definition </span> <span>return</span> <span>f</span><span>"</span><span>Hello, </span><span>{</span><span>name</span><span>}</span><span>!</span><span>"</span> <span>print</span><span>(</span><span>greet</span><span>(</span><span>"</span><span>Alice</span><span>"</span><span>))</span> <span># Calling the function </span>def greet(name): # Function definition return f"Hello, {name}!" print(greet("Alice")) # Calling the function
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Function Arguments and Return Values
Python functions support different types of arguments:
1. Positional Arguments
<span>def</span> <span>add</span><span>(</span><span>a</span><span>,</span> <span>b</span><span>):</span><span>return</span> <span>a</span> <span>+</span> <span>b</span><span>print</span><span>(</span><span>add</span><span>(</span><span>5</span><span>,</span> <span>3</span><span>))</span> <span># Output: 8 </span><span>def</span> <span>add</span><span>(</span><span>a</span><span>,</span> <span>b</span><span>):</span> <span>return</span> <span>a</span> <span>+</span> <span>b</span> <span>print</span><span>(</span><span>add</span><span>(</span><span>5</span><span>,</span> <span>3</span><span>))</span> <span># Output: 8 </span>def add(a, b): return a + b print(add(5, 3)) # Output: 8
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2. Default Arguments
<span>def</span> <span>power</span><span>(</span><span>base</span><span>,</span> <span>exponent</span><span>=</span><span>2</span><span>):</span> <span># Default value for exponent </span> <span>return</span> <span>base</span> <span>**</span> <span>exponent</span><span>print</span><span>(</span><span>power</span><span>(</span><span>3</span><span>))</span> <span># Output: 9 (3^2) </span><span>print</span><span>(</span><span>power</span><span>(</span><span>3</span><span>,</span> <span>3</span><span>))</span> <span># Output: 27 (3^3) </span><span>def</span> <span>power</span><span>(</span><span>base</span><span>,</span> <span>exponent</span><span>=</span><span>2</span><span>):</span> <span># Default value for exponent </span> <span>return</span> <span>base</span> <span>**</span> <span>exponent</span> <span>print</span><span>(</span><span>power</span><span>(</span><span>3</span><span>))</span> <span># Output: 9 (3^2) </span><span>print</span><span>(</span><span>power</span><span>(</span><span>3</span><span>,</span> <span>3</span><span>))</span> <span># Output: 27 (3^3) </span>def power(base, exponent=2): # Default value for exponent return base ** exponent print(power(3)) # Output: 9 (3^2) print(power(3, 3)) # Output: 27 (3^3)
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3. Keyword Arguments (Named Arguments)
<span>def</span> <span>introduce</span><span>(</span><span>name</span><span>,</span> <span>age</span><span>):</span><span>print</span><span>(</span><span>f</span><span>"</span><span>My name is </span><span>{</span><span>name</span><span>}</span><span> and I</span><span>'</span><span>m </span><span>{</span><span>age</span><span>}</span><span> years old.</span><span>"</span><span>)</span><span>introduce</span><span>(</span><span>age</span><span>=</span><span>25</span><span>,</span> <span>name</span><span>=</span><span>"</span><span>Bob</span><span>"</span><span>)</span> <span># Order doesn't matter </span><span>def</span> <span>introduce</span><span>(</span><span>name</span><span>,</span> <span>age</span><span>):</span> <span>print</span><span>(</span><span>f</span><span>"</span><span>My name is </span><span>{</span><span>name</span><span>}</span><span> and I</span><span>'</span><span>m </span><span>{</span><span>age</span><span>}</span><span> years old.</span><span>"</span><span>)</span> <span>introduce</span><span>(</span><span>age</span><span>=</span><span>25</span><span>,</span> <span>name</span><span>=</span><span>"</span><span>Bob</span><span>"</span><span>)</span> <span># Order doesn't matter </span>def introduce(name, age): print(f"My name is {name} and I'm {age} years old.") introduce(age=25, name="Bob") # Order doesn't matter
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4. Arbitrary Arguments (args and kwargs)
<span>def</span> <span>multiply</span><span>(</span><span>*</span><span>args</span><span>):</span> <span># Accepts multiple arguments </span> <span>result</span> <span>=</span> <span>1</span><span>for</span> <span>num</span> <span>in</span> <span>args</span><span>:</span><span>result</span> <span>*=</span> <span>num</span><span>return</span> <span>result</span><span>print</span><span>(</span><span>multiply</span><span>(</span><span>2</span><span>,</span> <span>3</span><span>,</span> <span>4</span><span>))</span> <span># Output: 24 </span><span>def</span> <span>describe_person</span><span>(</span><span>**</span><span>kwargs</span><span>):</span> <span># Accepts key-value pairs </span> <span>for</span> <span>key</span><span>,</span> <span>value</span> <span>in</span> <span>kwargs</span><span>.</span><span>items</span><span>():</span><span>print</span><span>(</span><span>f</span><span>"</span><span>{</span><span>key</span><span>}</span><span>: </span><span>{</span><span>value</span><span>}</span><span>"</span><span>)</span><span>describe_person</span><span>(</span><span>name</span><span>=</span><span>"</span><span>Alice</span><span>"</span><span>,</span> <span>age</span><span>=</span><span>30</span><span>,</span> <span>country</span><span>=</span><span>"</span><span>USA</span><span>"</span><span>)</span><span>def</span> <span>multiply</span><span>(</span><span>*</span><span>args</span><span>):</span> <span># Accepts multiple arguments </span> <span>result</span> <span>=</span> <span>1</span> <span>for</span> <span>num</span> <span>in</span> <span>args</span><span>:</span> <span>result</span> <span>*=</span> <span>num</span> <span>return</span> <span>result</span> <span>print</span><span>(</span><span>multiply</span><span>(</span><span>2</span><span>,</span> <span>3</span><span>,</span> <span>4</span><span>))</span> <span># Output: 24 </span> <span>def</span> <span>describe_person</span><span>(</span><span>**</span><span>kwargs</span><span>):</span> <span># Accepts key-value pairs </span> <span>for</span> <span>key</span><span>,</span> <span>value</span> <span>in</span> <span>kwargs</span><span>.</span><span>items</span><span>():</span> <span>print</span><span>(</span><span>f</span><span>"</span><span>{</span><span>key</span><span>}</span><span>: </span><span>{</span><span>value</span><span>}</span><span>"</span><span>)</span> <span>describe_person</span><span>(</span><span>name</span><span>=</span><span>"</span><span>Alice</span><span>"</span><span>,</span> <span>age</span><span>=</span><span>30</span><span>,</span> <span>country</span><span>=</span><span>"</span><span>USA</span><span>"</span><span>)</span>def multiply(*args): # Accepts multiple arguments result = 1 for num in args: result *= num return result print(multiply(2, 3, 4)) # Output: 24 def describe_person(**kwargs): # Accepts key-value pairs for key, value in kwargs.items(): print(f"{key}: {value}") describe_person(name="Alice", age=30, country="USA")
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2️⃣ Lambda Functions: One-Liner Functions
Lambda functions are anonymous, inline functions used for short operations.
Basic Syntax:
lambda arguments: expression
Example:
<span>square</span> <span>=</span> <span>lambda</span> <span>x</span><span>:</span> <span>x</span> <span>**</span> <span>2</span><span>print</span><span>(</span><span>square</span><span>(</span><span>4</span><span>))</span> <span># Output: 16 </span><span>add</span> <span>=</span> <span>lambda</span> <span>a</span><span>,</span> <span>b</span><span>:</span> <span>a</span> <span>+</span> <span>b</span><span>print</span><span>(</span><span>add</span><span>(</span><span>3</span><span>,</span> <span>5</span><span>))</span> <span># Output: 8 </span><span>square</span> <span>=</span> <span>lambda</span> <span>x</span><span>:</span> <span>x</span> <span>**</span> <span>2</span> <span>print</span><span>(</span><span>square</span><span>(</span><span>4</span><span>))</span> <span># Output: 16 </span> <span>add</span> <span>=</span> <span>lambda</span> <span>a</span><span>,</span> <span>b</span><span>:</span> <span>a</span> <span>+</span> <span>b</span> <span>print</span><span>(</span><span>add</span><span>(</span><span>3</span><span>,</span> <span>5</span><span>))</span> <span># Output: 8 </span>square = lambda x: x ** 2 print(square(4)) # Output: 16 add = lambda a, b: a + b print(add(3, 5)) # Output: 8
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Use Case: Lambda functions are often used in sorting, filtering, and mapping data.
<span>numbers</span> <span>=</span> <span>[</span><span>3</span><span>,</span> <span>1</span><span>,</span> <span>4</span><span>,</span> <span>1</span><span>,</span> <span>5</span><span>,</span> <span>9</span><span>]</span><span>sorted_numbers</span> <span>=</span> <span>sorted</span><span>(</span><span>numbers</span><span>,</span> <span>key</span><span>=</span><span>lambda</span> <span>x</span><span>:</span> <span>-</span><span>x</span><span>)</span> <span># Sort in descending order </span><span>print</span><span>(</span><span>sorted_numbers</span><span>)</span> <span># Output: [9, 5, 4, 3, 1, 1] </span><span>numbers</span> <span>=</span> <span>[</span><span>3</span><span>,</span> <span>1</span><span>,</span> <span>4</span><span>,</span> <span>1</span><span>,</span> <span>5</span><span>,</span> <span>9</span><span>]</span> <span>sorted_numbers</span> <span>=</span> <span>sorted</span><span>(</span><span>numbers</span><span>,</span> <span>key</span><span>=</span><span>lambda</span> <span>x</span><span>:</span> <span>-</span><span>x</span><span>)</span> <span># Sort in descending order </span><span>print</span><span>(</span><span>sorted_numbers</span><span>)</span> <span># Output: [9, 5, 4, 3, 1, 1] </span>numbers = [3, 1, 4, 1, 5, 9] sorted_numbers = sorted(numbers, key=lambda x: -x) # Sort in descending order print(sorted_numbers) # Output: [9, 5, 4, 3, 1, 1]
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3️⃣ Introduction to Object-Oriented Programming (OOP)
OOP is a programming paradigm that models real-world entities using classes and objects.
Why Use OOP?
Encapsulation – Grouping related data and functions together
Inheritance – Reusing and extending functionality
Polymorphism – Writing flexible code that works across different types
4️⃣ Classes and Objects in Python**
Defining a Class and Creating Objects
<span>class</span> <span>Person</span><span>:</span><span>def</span> <span>__init__</span><span>(</span><span>self</span><span>,</span> <span>name</span><span>,</span> <span>age</span><span>):</span> <span># Constructor </span> <span>self</span><span>.</span><span>name</span> <span>=</span> <span>name</span> <span># Instance variable </span> <span>self</span><span>.</span><span>age</span> <span>=</span> <span>age</span><span>def</span> <span>introduce</span><span>(</span><span>self</span><span>):</span> <span># Method </span> <span>return</span> <span>f</span><span>"</span><span>My name is </span><span>{</span><span>self</span><span>.</span><span>name</span><span>}</span><span> and I</span><span>'</span><span>m </span><span>{</span><span>self</span><span>.</span><span>age</span><span>}</span><span> years old.</span><span>"</span><span># Creating an object (instance) </span><span>alice</span> <span>=</span> <span>Person</span><span>(</span><span>"</span><span>Alice</span><span>"</span><span>,</span> <span>25</span><span>)</span><span>print</span><span>(</span><span>alice</span><span>.</span><span>introduce</span><span>())</span> <span># Output: My name is Alice and I'm 25 years old. </span><span>class</span> <span>Person</span><span>:</span> <span>def</span> <span>__init__</span><span>(</span><span>self</span><span>,</span> <span>name</span><span>,</span> <span>age</span><span>):</span> <span># Constructor </span> <span>self</span><span>.</span><span>name</span> <span>=</span> <span>name</span> <span># Instance variable </span> <span>self</span><span>.</span><span>age</span> <span>=</span> <span>age</span> <span>def</span> <span>introduce</span><span>(</span><span>self</span><span>):</span> <span># Method </span> <span>return</span> <span>f</span><span>"</span><span>My name is </span><span>{</span><span>self</span><span>.</span><span>name</span><span>}</span><span> and I</span><span>'</span><span>m </span><span>{</span><span>self</span><span>.</span><span>age</span><span>}</span><span> years old.</span><span>"</span> <span># Creating an object (instance) </span><span>alice</span> <span>=</span> <span>Person</span><span>(</span><span>"</span><span>Alice</span><span>"</span><span>,</span> <span>25</span><span>)</span> <span>print</span><span>(</span><span>alice</span><span>.</span><span>introduce</span><span>())</span> <span># Output: My name is Alice and I'm 25 years old. </span>class Person: def __init__(self, name, age): # Constructor self.name = name # Instance variable self.age = age def introduce(self): # Method return f"My name is {self.name} and I'm {self.age} years old." # Creating an object (instance) alice = Person("Alice", 25) print(alice.introduce()) # Output: My name is Alice and I'm 25 years old.
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Instance Variables vs. Class Variables
<span>class</span> <span>Counter</span><span>:</span><span>count</span> <span>=</span> <span>0</span> <span># Class variable (shared among all instances) </span><span>def</span> <span>__init__</span><span>(</span><span>self</span><span>):</span><span>Counter</span><span>.</span><span>count</span> <span>+=</span> <span>1</span><span>obj1</span> <span>=</span> <span>Counter</span><span>()</span><span>obj2</span> <span>=</span> <span>Counter</span><span>()</span><span>print</span><span>(</span><span>Counter</span><span>.</span><span>count</span><span>)</span> <span># Output: 2 (shared across all objects) </span><span>class</span> <span>Counter</span><span>:</span> <span>count</span> <span>=</span> <span>0</span> <span># Class variable (shared among all instances) </span> <span>def</span> <span>__init__</span><span>(</span><span>self</span><span>):</span> <span>Counter</span><span>.</span><span>count</span> <span>+=</span> <span>1</span> <span>obj1</span> <span>=</span> <span>Counter</span><span>()</span> <span>obj2</span> <span>=</span> <span>Counter</span><span>()</span> <span>print</span><span>(</span><span>Counter</span><span>.</span><span>count</span><span>)</span> <span># Output: 2 (shared across all objects) </span>class Counter: count = 0 # Class variable (shared among all instances) def __init__(self): Counter.count += 1 obj1 = Counter() obj2 = Counter() print(Counter.count) # Output: 2 (shared across all objects)
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Key Difference:
Instance Variables (self.name) are unique to each object.Class Variables (count) are shared across all instances.Instance Variables (self.name) are unique to each object. Class Variables (count) are shared across all instances.Instance Variables (self.name) are unique to each object. Class Variables (count) are shared across all instances.
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5️⃣ Inheritance: Reusing Code
Inheritance allows one class (child class) to inherit the properties of another (parent class).
<span>class</span> <span>Animal</span><span>:</span><span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span><span>return</span> <span>"</span><span>I make sounds</span><span>"</span><span>class</span> <span>Dog</span><span>(</span><span>Animal</span><span>):</span> <span># Dog class inherits from Animal </span> <span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span><span>return</span> <span>"</span><span>Woof!</span><span>"</span><span>dog</span> <span>=</span> <span>Dog</span><span>()</span><span>print</span><span>(</span><span>dog</span><span>.</span><span>speak</span><span>())</span> <span># Output: Woof! </span><span>class</span> <span>Animal</span><span>:</span> <span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span> <span>return</span> <span>"</span><span>I make sounds</span><span>"</span> <span>class</span> <span>Dog</span><span>(</span><span>Animal</span><span>):</span> <span># Dog class inherits from Animal </span> <span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span> <span>return</span> <span>"</span><span>Woof!</span><span>"</span> <span>dog</span> <span>=</span> <span>Dog</span><span>()</span> <span>print</span><span>(</span><span>dog</span><span>.</span><span>speak</span><span>())</span> <span># Output: Woof! </span>class Animal: def speak(self): return "I make sounds" class Dog(Animal): # Dog class inherits from Animal def speak(self): return "Woof!" dog = Dog() print(dog.speak()) # Output: Woof!
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6️⃣ Encapsulation: Hiding Data with Private Variables
Encapsulation prevents direct modification of attributes.
<span>class</span> <span>BankAccount</span><span>:</span><span>def</span> <span>__init__</span><span>(</span><span>self</span><span>,</span> <span>balance</span><span>):</span><span>self</span><span>.</span><span>__balance</span> <span>=</span> <span>balance</span> <span># Private variable (cannot be accessed directly) </span><span>def</span> <span>deposit</span><span>(</span><span>self</span><span>,</span> <span>amount</span><span>):</span><span>self</span><span>.</span><span>__balance</span> <span>+=</span> <span>amount</span><span>def</span> <span>get_balance</span><span>(</span><span>self</span><span>):</span><span>return</span> <span>self</span><span>.</span><span>__balance</span> <span># Provide controlled access </span><span>account</span> <span>=</span> <span>BankAccount</span><span>(</span><span>1000</span><span>)</span><span>account</span><span>.</span><span>deposit</span><span>(</span><span>500</span><span>)</span><span>print</span><span>(</span><span>account</span><span>.</span><span>get_balance</span><span>())</span> <span># Output: 1500 </span><span># print(account.__balance) # This will raise an AttributeError </span><span>class</span> <span>BankAccount</span><span>:</span> <span>def</span> <span>__init__</span><span>(</span><span>self</span><span>,</span> <span>balance</span><span>):</span> <span>self</span><span>.</span><span>__balance</span> <span>=</span> <span>balance</span> <span># Private variable (cannot be accessed directly) </span> <span>def</span> <span>deposit</span><span>(</span><span>self</span><span>,</span> <span>amount</span><span>):</span> <span>self</span><span>.</span><span>__balance</span> <span>+=</span> <span>amount</span> <span>def</span> <span>get_balance</span><span>(</span><span>self</span><span>):</span> <span>return</span> <span>self</span><span>.</span><span>__balance</span> <span># Provide controlled access </span> <span>account</span> <span>=</span> <span>BankAccount</span><span>(</span><span>1000</span><span>)</span> <span>account</span><span>.</span><span>deposit</span><span>(</span><span>500</span><span>)</span> <span>print</span><span>(</span><span>account</span><span>.</span><span>get_balance</span><span>())</span> <span># Output: 1500 </span> <span># print(account.__balance) # This will raise an AttributeError </span>class BankAccount: def __init__(self, balance): self.__balance = balance # Private variable (cannot be accessed directly) def deposit(self, amount): self.__balance += amount def get_balance(self): return self.__balance # Provide controlled access account = BankAccount(1000) account.deposit(500) print(account.get_balance()) # Output: 1500 # print(account.__balance) # This will raise an AttributeError
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7️⃣ Polymorphism: Methods with the Same Name but Different Behavior
<span>class</span> <span>Bird</span><span>:</span><span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span><span>return</span> <span>"</span><span>Chirp!</span><span>"</span><span>class</span> <span>Dog</span><span>:</span><span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span><span>return</span> <span>"</span><span>Woof!</span><span>"</span><span>animals</span> <span>=</span> <span>[</span><span>Bird</span><span>(),</span> <span>Dog</span><span>()]</span><span>for</span> <span>animal</span> <span>in</span> <span>animals</span><span>:</span><span>print</span><span>(</span><span>animal</span><span>.</span><span>speak</span><span>())</span> <span># Calls the correct method for each object </span><span>class</span> <span>Bird</span><span>:</span> <span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span> <span>return</span> <span>"</span><span>Chirp!</span><span>"</span> <span>class</span> <span>Dog</span><span>:</span> <span>def</span> <span>speak</span><span>(</span><span>self</span><span>):</span> <span>return</span> <span>"</span><span>Woof!</span><span>"</span> <span>animals</span> <span>=</span> <span>[</span><span>Bird</span><span>(),</span> <span>Dog</span><span>()]</span> <span>for</span> <span>animal</span> <span>in</span> <span>animals</span><span>:</span> <span>print</span><span>(</span><span>animal</span><span>.</span><span>speak</span><span>())</span> <span># Calls the correct method for each object </span>class Bird: def speak(self): return "Chirp!" class Dog: def speak(self): return "Woof!" animals = [Bird(), Dog()] for animal in animals: print(animal.speak()) # Calls the correct method for each object
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Why Polymorphism?
Allows different classes to share the same method name, making code more flexible.
Conclusion
Functions improve reusability and structure.
Lambda functions allow writing concise, one-liner expressions.
OOP (Classes, Inheritance, Encapsulation, Polymorphism) models real-world entities effectively.
Mastering these concepts will help you write cleaner and more maintainable Python code.
What’s Next?
In the next post, we’ll explore Python’s Modules and Packages, learning how to organize code effectively. Stay tuned!
What Do You Think?
Do you use OOP in your projects? What’s your favorite Python feature? Let’s discuss in the comments!
原文链接：Functions and Object-Oriented Programming (OOP) in Python
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