Unit 2function in python.pptx

Unit 2: functions in Python
21BCA2T452 : Python Programming
Prof. Vishnu Priya P M
Assistant Professor Dept. of Computer Science
Kristu Jayanti College, Autonomous
(Reaccredited A++ Grade by NAAC with CGPA 3.78/4)
Bengaluru – 560077, India

FUNCTION
Function in Python is a reusable block of code that performs a specific task. It allows you to
encapsulate a set of instructions into a single unit, which you can then call by its name whenever
you want to execute that set of instructions. Functions provide modularity, reusability, and
organization to your code.
In Python, you can define a function using the def keyword followed by the function name, a set
of parentheses containing any parameters the function takes, and a colon. The function body is
indented and contains the code that defines what the function does. You can also include a return
statement to send a value back as the result of the function's execution.
def greet(name):
return "Hello, " + name + "!"
# Calling the function
message = greet("Alice")
print(message) # Output: Hello,
Alice! the greet function takes a single parameter name and returns a greeting
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USER-DEFINED FUNCTIONS IN PYTHON
User-defined functions in Python are functions that you create yourself to perform specific
tasks according to your needs. They allow you to encapsulate a block of code into a reusable
unit, making your code more organized and modular.
To define a user-defined function in Python, you use the def keyword followed by the function
name, a set of parentheses containing any parameters the function takes (if any), and a colon. The
function body is indented and contains the code that defines what the function does. You can also
include a return statement to send a value back as the result of the function's execution.
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Here's the basic syntax for defining a user-defined function:
def function_name(parameters):
# Function body
# Code to perform the task
return result # Optional
Here's an example of a simple user-defined function:
def add_numbers(a, b):
return a + b
result = add_numbers(5, 3)
print(result) # Output: 8
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the add_numbers function takes two parameters a and b, and returns their sum.
User-defined functions can have multiple parameters, and those parameters can have default
values. You can call a user-defined function by providing the required arguments in the same order
as the function definition, or by using keyword arguments to specify which parameter you're
providing a value for.
Here's an example with default parameters and keyword arguments:
def greet(name, message="Hello"):
return f"{message}, {name}!"
print(greet("Alice")) # Output: Hello, Alice!
print(greet("Bob", message="Hi")) # Output: Hi, Bob!
User-defined functions can be as simple or as complex as you need them to be, and they greatly enhance the
reusability and readability of your code.
#formatted string is constructed using an f-string.
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ANONYMOUS FUNCTIONS
Anonymous functions are known as "lambda" functions. A lambda function is a small, inline
function that doesn't have a formal name like a regular user-defined function. Lambda functions
are often used for short, simple operations that can be defined in a single line of code.
The syntax for creating a lambda function is as follows:
lambda arguments: expression
Here's a basic example of a lambda function that adds two numbers:
add = lambda x, y: x + y
result = add(5, 3)
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Lambda functions are typically used when you need a quick function for a short task, like passing a function as
an argument to another function, working with higher-order functions like map(), filter(), or sorted(), or creating
simple key functions for sorting.
Here's an example of using a lambda function with the sorted() function:
points = [(3, 5), (1, 9), (8, 2)]
sorted_points = sorted(points, key=lambda point: point[1]) #Sorting by the second element of each tuple
print(sorted_points) # Output: [(8, 2), (3, 5), (1, 9)]
Lambda functions can be useful in situations where defining a full named function might be unnecessary due to
the function's simplicity. However, for more complex or larger functions, it's generally better to use regular user-
defined functions for clarity and maintainability.
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RECURSIVE FUNCTIONS
 Recursive function is a function that calls itself as part of its execution.
 Recursive functions are used to solve problems that can be broken down into
smaller instances of the same problem.
 Each recursive call works on a smaller piece of the problem until it reaches a
base case where a direct solution can be obtained without further recursion.
 Recursive functions can be a powerful tool for solving certain types of
problems, but they should be designed carefully to avoid infinite recursion and
excessive function calls.
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calculating the factorial of a non-negative integer n:
def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n - 1)
result = factorial(5) # 5! = 5 * 4 * 3 * 2 * 1 = 120
The factorial function calls itself with a smaller value
of n until it reaches the base case where n is 0. This
base case returns 1, and the function then starts
"unwinding" the recursive calls, multiplying each
value of n until the original call is complete.
When creating recursive functions, it's important to define the base case(s) that will terminate the
recursion and prevent infinite loops. Without a proper base case, the function would keep calling
itself indefinitely and eventually lead to a "RecursionError" due to exceeding the maximum recursion
depth.
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Calculating the Fibonacci sequence:
def fibonacci(n):
if n <= 0:
return 0
elif n == 1:
return 1
else:
return fibonacci(n - 1) + fibonacci(n - 2)
result = fibonacci(6) # Fibonacci sequence: 0, 1, 1, 2, 3, 5, ...
The fibonacci function calculates the nth number in the
Fibonacci sequence by recursively summing the previous
two numbers.
Recursive functions can be elegant solutions for certain problems, but they can also be less efficient than
iterative approaches in terms of memory and performance. When using recursion, it's important to
understand the trade-offs and choose the appropriate approach based on the problem's requirements.
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INTRODUCTION TO MODULES
A module is a file containing Python definitions, functions, classes, and
variables that can be used in other Python programs. Modules provide a way
to organize your code and make it more modular, reusable, and
maintainable. Python has a rich collection of built-in modules, and you can also
create your own custom modules to encapsulate related functionality.
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Introduction to working with modules in Python:
1. Built-in Modules: Python comes with a set of built-in modules that provide various
functionalities. Some common examples include:
a. math: Provides mathematical functions and constants.
b. random: Generates random numbers.
c. datetime: Manipulates dates and times.
d. os: Interacts with the operating system, like reading directories and files.
e. sys: Provides access to system-specific parameters and functions.
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2. Importing Modules: To use functions, classes, or variables from a module, you need to import the
module into your code. The import statement is used for this purpose. For example:
import math
print(math.sqrt(16)) # Output: 4.0
You can also use the from keyword to import specific items from a module:
from math import sqrt
print(sqrt(16)) # Output: 4.0
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3. Creating Custom Modules: You can create your own modules by creating a .py file and placing
your Python code inside it. For example, if you create a file named my_module.py with the following
content:
def greet(name):
return f"Hello, {name}!"
You can then use this module in another script:
import my_module
message = my_module.greet("Alice")
print(message) # Output: Hello, Alice!
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4. Package: A package is a collection of related modules organized in a directory hierarchy. It
includes a special __init__.py file that makes Python treat the directory as a package. Packages
allow you to organize related modules into a coherent structure.
5. Third-party Modules: Python has a vast ecosystem of third-party modules that you can install and
use to extend your code's functionality. You can install these modules using tools like pip (Python
package manager).
pip install module_name
Common third-party modules include numpy, pandas, requests, and many others.
Using modules in Python promotes code reusability and helps manage the complexity of larger
projects. By breaking down your code into smaller, modular components, you can work more
efficiently and collaborate effectively with other developers.
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CREATING AND IMPORTING AND MODULES IN PYTHON
Creating and importing modules in Python is a fundamental concept for organizing your code and
making it more modular.
Step 1: Create a Module
1. Create a new file and give it a meaningful name with a .py extension. For example, let's create a
module named my_module.py.
2. Inside my_module.py, define functions, classes, or variables that you want to include in your
module. Here's an example:
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def greet(name):
return f"Hello, {name}!"
def square(x):
return x ** 2
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Step 2: Save the Module
Save the my_module.py file in the same directory as your main script or in a location where Python
can find it (e.g., a directory included in the sys.path list).
Step 3: Import and Use the Module
Now, you can import and use the module in another Python script.
1. Create a new Python script (e.g., main_script.py) in the same directory as the my_module.py
module.
2. Import the module using the import statement:
import my_module
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3. Use functions from the module in your script:
message = my_module.greet("Alice")
print(message) # Output: Hello, Alice!
result = my_module.square(5)
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Step 4: Run the Script
Run the main_script.py script using your Python interpreter. You should see the output
corresponding to the imported functions.
Note that you can also use the from ... import ... syntax to import specific functions or variables
from the module directly into your script's namespace:
from my_module import greet
message = greet("Bob")
print(message) # Output: Hello, Bob!
Keep in mind that the name of the module (e.g., my_module) acts as a namespace for the functions and
variables defined within it. This helps prevent naming conflicts between different modules.
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CLASSES AND OBJECTS
A class is a blueprint or template for creating objects. It defines the attributes (data) and methods
(functions) that objects of that class will have. In Python, you define a class using the class keyword
followed by the class name and a colon. The attributes and methods are defined within the class's
body. class Dog:
def __init__(self, name, age):
self.name = name
self.age = age
def bark(self):
return "Woof!"
In this example, we've defined a Dog class with attributes name and age, and a method bark()
Class
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Object:
An object is an instance of a class. It's a concrete entity that can hold data (attributes) and perform
actions (methods) as defined by the class. To create an object, you call the class as if it were a
function, which creates a new instance of that class.
my_dog = Dog("Buddy", 3)
In this case, my_dog is an object of the Dog class with the name attribute set to "Buddy" and the age
attribute set to 3.
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Using Objects:
You can access the attributes and methods of an object using the dot (.) notation:
print(my_dog.name) # Output: Buddy
print(my_dog.age) # Output: 3
print(my_dog.bark()) # Output: Woof!
Constructor (__init__ method):
The __init__ method is a special method called a constructor. It's used to initialize the attributes of an
object when it's created. The self parameter refers to the object itself and is used to access its
attributes and methods.
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Methods:
Methods are functions defined within a class. They operate on the attributes of the object and can
perform various actions. Methods often take the self parameter as the first parameter, which refers
to the instance of the class.
class Dog:
self.name = name
self.age = age
def bark(self):
return "Woof!"
def describe(self):
return f"{self.name} is {self.age} years old."
the describe() method provides a way to get a description of the
dog.
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CLASS PROPERTIES
class properties are attributes associated with a class that have special behavior when accessed or
modified. They provide a way to encapsulate and control the access to class-level data.
There are two main types of class properties:
class variables and class methods.
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Class Variables:
Class variables are shared among all instances of a class. They are defined within
the class scope but outside any methods. Class variables are accessible using the
class name and can also be accessed through instances of the class. They are
often used to store data that is common to all instances of the class.
class MyClass:
class_variable = 0 # This is a class variable
def __init__(self, value):
self.instance_variable = value
obj1 = MyClass(10)
obj2 = MyClass(20)
print(obj1.class_variable) # Output: 0
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Class Methods:
Class methods are methods defined within a class that are bound to the class
rather than instances. They are defined using the @classmethod decorator and
receive the class as their first argument (often named cls by convention). Class
methods are typically used to perform operations that are related to the class
itself rather than instances. class MyClass:
class_variable = 0
def __init__(self, value):
self.instance_variable = value
@classmethod
def modify_class_variable(cls, new_value):
cls.class_variable = new_value
obj1 = MyClass(10)
obj2 = MyClass(20)
obj1.modify_class_variable(5)
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STATIC METHOD
static method is a method that belongs to a class but is not bound to instances of
that class. It's defined within the class, but it doesn't receive the class or instance
as an implicit first parameter (like instance methods or class methods do). Instead,
it behaves like a regular function, except it's namespaced within the class.
Static methods are typically used for utility functions that are related to the class
in some way but don't depend on or modify instance or class-specific data. They
are defined using the @staticmethod decorator and do not require access to
instance or class-specific information.
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class MathUtils:
@staticmethod
def add(x, y):
return x + y
@staticmethod
def subtract(x, y):
return x - y
result1 = MathUtils.add(5, 3)
result2 = MathUtils.subtract(10, 2)
print(result1) # Output: 8
print(result2) # Output: 8
In this example, the add and subtract methods are static
methods because they don't access any instance-specific
or class-specific data. They perform basic arithmetic
operations and are associated with the MathUtils class, but
they can be called using the class name without creating
instances of the class.
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CONSTRUCTOR
Constructor is a special method that gets automatically called when an object of a class is created.
It's used to initialize the attributes (properties) of the object. The constructor method is named
__init__ and is defined within the class.
class Person:
self.name = name
self.age = age
# Creating objects using the constructor
person1 = Person("Alice", 30)
person2 = Person("Bob", 25)
# Accessing object attributes
print(person1.name) # Output: Alice
print(person1.age) # Output: 30
print(person2.name) # Output: Bob
print(person2.age) # Output: 25
the __init__ method is the constructor for the Person class.
It takes two parameters, name and age, and initializes the
corresponding attributes of the object being created using
those values.
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Key points about constructors in Python:
 The constructor method is named __init__.
 The first parameter of the constructor is conventionally named self, which
refers to the instance being created.
 The constructor is automatically called when an object of the class is created
using the class name followed by parentheses, like a function call.
 You can pass arguments to the constructor that will be used to initialize the
object's attributes.
 Inside the constructor, you can assign values to attributes using the self
keyword.
 Constructors can have any number of parameters, not just self, and can
perform any necessary initialization.
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METHOD OVERRIDING
Method overriding in Python allows a subclass to provide a specific
implementation for a method that is already defined in its parent class. This
enables you to customize the behavior of methods in the subclass while
maintaining the same method signature as the parent class. Method overriding is
a key feature of polymorphism in object-oriented programming.
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How method overriding works
• Method Signature:
To override a method, the subclass method must have the same name and
parameters as the method in the parent class. The method in the subclass should
be defined with the same method signature as the one in the parent class.
• Using the super() Function:
Inside the overridden method of the subclass, you can use the super() function to
call the corresponding method of the parent class. This allows you to extend or
modify the behavior of the parent class method without completely replacing it.
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class Animal:
def speak(self):
return "Animal speaks"
class Dog(Animal):
def speak(self):
return "Woof"
class Cat(Animal):
def speak(self):
return "Meow"
animal = Animal()
dog = Dog()
cat = Cat()
print(animal.speak()) # Output: Animal speaks
print(dog.speak()) # Output: Woof
print(cat.speak()) # Output: Meow
the speak method is overridden in both the Dog and Cat
classes. Each subclass provides its own implementation of
the method, allowing them to exhibit different behaviors
while sharing the same method name.
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Key points about method overriding :
 Method overriding allows a subclass to provide a custom implementation for
a method defined in its parent class.
 The subclass method must have the same name and parameters as the
method in the parent class.
 The super() function is used to call the parent class method within the
overridden method.
 Overriding methods enables you to achieve polymorphism, where objects of
different subclasses can be treated uniformly through their common interface
(method names).
 Overriding methods in Python is a way to implement the "Liskov Substitution
Principle," which is one of the SOLID principles of object-oriented design.
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class Animal(object):
def __init__(self, animal_type):
print('Animal Type:', animal_type)
class Mammal(Animal):
def __init__(self):
# call superclass
super().__init__('Mammal')
print('Mammals give birth directly')
dog = Mammal()
# Output: Animal Type: Mammal
# Mammals give birth directly
super()

INHERITANCE
Inheritance is a fundamental concept in object-oriented programming (OOP) that allows you to
create a new class (subclass or derived class) based on an existing class (superclass or base class).
The new class inherits attributes and methods from the existing class, and you can also add new
attributes and methods or override existing ones in the subclass. Inheritance promotes code
reuse, modularity, and the organization of code into a hierarchy.
you can create a subclass by defining a new class and specifying the superclass in parentheses
after the class name.
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class Animal:
def __init__(self, name):
self.name = name
def speak(self):
return "Animal speaks"
class Dog(Animal):
def speak(self):
return "Woof"
class Cat(Animal):
def speak(self):
return "Meow"
dog = Dog("Buddy")
cat = Cat("Whiskers")
print(dog.name) # Output: Buddy
print(dog.speak()) # Output: Woof
print(cat.name) # Output: Whiskers
print(cat.speak()) # Output: Meow
Animal is the base class, and Dog and Cat are subclasses
that inherit from Animal. The subclasses override the
speak method to provide their own implementations,
while still inheriting the __init__ method and attribute from
the Animal class.
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Key points about inheritance in Python:
 The base class is also known as the superclass or parent class.
 The derived class is also known as the subclass or child class.
 The subclass inherits attributes and methods from the superclass.
 You can add new attributes and methods to the subclass, or override existing
ones.
 Inheritance supports the "is-a" relationship, where a subclass is a specific type of
the superclass.
 Python supports multiple inheritance, allowing a class to inherit from multiple
parent classes.
 The super() function is commonly used to call methods from the parent class
within overridden methods.
 Inheritance promotes code reuse, modularity, and the creation of hierarchical
class structures.
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OPERATOR OVERLOADING
Operator overloading refers to the ability to define custom behavior for standard operators (+, -, *, /, etc.)
when used with objects of user-defined classes. This allows you to make your objects behave more like built-in
types, providing a more intuitive and natural interface.
To overload an operator for a user-defined class, you need to define special methods with specific names that
Python recognizes. These methods are also called "magic methods" or "dunder methods" (short for "double
underscore" methods). They have names that start and end with double underscores, such as __add__ for the
addition operator.
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class Point:
def __init__(self, x, y):
self.x = x
self.y = y
def __add__(self, other):
if isinstance(other, Point):
return Point(self.x + other.x, self.y + other.y)
else:
raise TypeError("Unsupported operand type")
def __str__(self):
return f"({self.x}, {self.y})"
# Create points
p1 = Point(1, 2)
p2 = Point(3, 4)
# Use the overloaded + operator
result = p1 + p2
print(result) # Output: (4, 6)
we've overloaded the + operator by defining the __add__
method in the Point class. When the + operator is used
between two Point objects, the __add__ method is called,
and we perform addition element-wise on the x and y
coordinates.
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INTRODUCTION TO PIP
pip is the package installer for Python. It's a command-line tool that allows you to install and
manage Python packages, which are pre-written libraries or modules that provide specific
functionality and can be easily reused in your own projects. Python packages are typically
published and shared on the Python Package Index (PyPI), a repository of open-source Python
packages.
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1. Installation:
If you're using a recent version of Python (Python 2.7.9+ or Python 3.4+), pip is usually already
installed. You can check if pip is installed by running pip --version in your terminal. If it's not
installed, you can install it by following the instructions on the official pip documentation.
2. Installing Packages:
To install a Python package using pip, you use the command pip install package_name. For
example, to install the popular requests package, you would run:
pip install requests
3. Listing Installed Packages:
You can list the packages installed in your Python environment using the command:
pip list
4. Uninstalling Packages:
To uninstall a package, you use the command pip uninstall package_name
pip uninstall requests
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5. Specifying Package Versions:
You can specify a particular version of a package to install by including the version number after the package
name. For example:
pip install requests==2.25.1
6. Requirements Files:
You can create a requirements.txt file listing all the packages required for your project, along with their
versions. This is useful for sharing project dependencies with others or for recreating the same environment
later. You can generate a requirements file using:
pip freeze > requirements.txt
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7. Installing from a Requirements File:
To install packages from a requirements file, you use the command:
pip install -r requirements.txt
8. Upgrading Packages:
To upgrade a package to the latest version, use the command:
pip install --upgrade package_name
9. Searching for Packages:
You can search for packages on PyPI using the command:
pip search search_term
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10. Virtual Environments:
It's recommended to use virtual environments to isolate your project's dependencies from the system-wide
Python installation. You can create a virtual environment using venv (for Python 3.3+) or virtualenv (for earlier
versions).
pip is a powerful tool that simplifies the process of managing Python packages and their dependencies,
making it easier to work on projects that rely on various external libraries. It's a standard tool used by Python
developers for creating consistent and reproducible development environments.
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