First Class functions in Python

In Python, functions are treated as first-class objects. This means they can be used just like numbers, strings, or any other variable. You can:

• Assign functions to variables.
• Pass them as arguments to other functions.
• Return them from functions.
• Store them in data structures such as lists or dictionaries.

This ability allows you to write reusable, modular and powerful code.

Characteristics of First-Class Functions

Functions in Python have the following important characteristics. Let’s see them one by one with examples:

1. Assigning Functions to Variables

We can assign a function to a variable and use the variable to call the function.

Example:

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

# Assigning the function to a variable
f = msg

# Calling the function using the variable
print(f("Emma"))  

Hello, Emma!

Explanation:

• The function msg is assigned to the variable f.
• Now f can be used to call msg, showing that functions behave like variables.

2. Passing Functions as Arguments

Functions can be passed as arguments to other functions, enabling higher-order functions.

Example:

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

def fun1(fun2, name):
    return fun2(name)

# Passing the msg function as an argument
print(fun1(msg, "Alex"))  

Hello, Alex!

Explanation:

• The function fun1 takes another function (fun2) as input.
• msg is passed to fun1, which then calls it with "Alex".

3. Returning Functions from Other Functions

A function can return another function, allowing for the creation of function factories.

Example:

def fun1(msg):
    def fun2():
        return f"Message: {msg}"
    return fun2

# Getting the inner function
func = fun1("Hello, World!")
print(func()) 

Message: Hello, World!

Explanation:

• The function fun1 defines another function fun2 and returns it.
• func stores the returned function fun2, which can be executed later.

4. Storing Functions in Data Structures

Functions can be stored in data structures like lists or dictionaries.

Example:

def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

# Storing functions in a dictionary
d = {
    "add": add,
    "subtract": subtract
}

# Calling functions from the dictionary
print(d["add"](5, 3))       
print(d["subtract"](5, 3)) 

8
2

Explanation:

• Functions add and subtract are stored in a dictionary.
• They are accessed using their keys and executed directly.