Definition and declaration

Definition in Python

A definition in Python refers to the creation of a variable, function, class, or any other data structure. It includes assigning values to variables, defining the body of functions, methods, or classes. Essentially, defining something means providing its complete structure and behavior.

Variable Definition

x = 10
y = "Hello, World!"

Function Definition

def greet(name):
    return f"Hello, {name}!"

Class Definition

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def get_info(self):
        return f"{self.name} is {self.age} years old."

List Definition

my_list = [1, 2, 3, 4, 5]

Declaration in Python

In some programming languages, a declaration refers to announcing the existence of a variable, function, or class without necessarily providing its complete definition. However, in Python, the concept of declaration is less explicit because Python is dynamically typed and does not require variable type declarations.

Combining Definition and Declaration in Python

In Python, defining a variable or function also serves as its declaration because you don’t separately declare their types.

Variable Definition (which also declares it)

count = 0
message = "Welcome to Python!"

Function Definition (which also declares it)

def add(a, b):
    return a + b

Class Definition (which also declares it)

class Animal:
    def __init__(self, species):
        self.species = species

    def speak(self):
        return "Some generic sound"

Key Points to Remember

Dynamic Typing: Python does not require explicit type declarations because it uses dynamic typing. The type of a variable is determined at runtime.

No Separate Declarations: Unlike some other languages (like C or Java), Python does not have separate variable or function declarations. Definitions in Python inherently serve as declarations.

Implicit Declaration: When you define a variable, function, or class in Python, you implicitly declare it.