Python Academy · Lesson

First-Class Functions

Pass and return functions.

Lesson 1 of 413 steps

First-Class Functions is a free Python Academy lesson on CoddyKit. This is lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Python Academy learning path, and your progress syncs across the web and the CoddyKit app. The Python Academy course includes 4 lessons in total.

Functions are objects

In Python, functions are first-class objects. They can be assigned to variables, stored in data structures, passed as arguments, and returned from other functions — just like numbers or strings.

def greet():
    return 'hi'
print(type(greet))
print(greet())

Assigning functions to variables

A function name is just a reference. Assign it to another name and call through that name — no parentheses when referring to the function itself.

def shout(text):
    return text.upper()
yell = shout
print(yell('hello'))

Functions in data structures

You can store functions in lists or dicts, then look them up and call them dynamically.

def add(a, b):
    return a + b
def sub(a, b):
    return a - b
ops = {'+': add, '-': sub}
print(ops['+'](10, 4))
print(ops['-'](10, 4))

Passing functions as arguments

A function that takes another function as a parameter is called a higher-order function. The passed function is the argument.

def apply(func, value):
    return func(value)
print(apply(str.upper, 'cat'))
print(apply(len, 'cat'))

map uses first-class functions

Built-ins like map rely on passing functions around. Here a function is applied to every item.

def square(n):
    return n * n
result = list(map(square, [1, 2, 3, 4]))
print(result)

filter takes a predicate

filter keeps items for which the passed function returns True. The function decides what stays.

def is_even(n):
    return n % 2 == 0
print(list(filter(is_even, range(10))))

Returning a function

A function can return another function. The returned function can then be called separately.

def get_greeter():
    def greeter(name):
        return 'Hello ' + name
    return greeter
f = get_greeter()
print(f('Ada'))

Functions as sort keys

sorted accepts a key function that maps each item to a value used for ordering.

words = ['banana', 'fig', 'cherry']
by_length = sorted(words, key=len)
print(by_length)

Lambdas as quick functions

A lambda is a small anonymous function. It is perfect for one-off use as an argument.

nums = [5, 1, 4, 2]
print(sorted(nums, key=lambda x: -x))

Functions have attributes

Since functions are objects, they carry attributes like __name__ and a docstring in __doc__.

def hello():
    'Says hello.'
    return 'hi'
print(hello.__name__)
print(hello.__doc__)

Building a dispatch table

Combining these ideas, you can build a clean dispatch table that picks a function by name — no long if/elif chains.

def start():
    return 'starting'
def stop():
    return 'stopping'
actions = {'start': start, 'stop': stop}
command = 'start'
print(actions[command]())

Quick Check

What does it mean that functions are 'first-class' in Python?

Answer it in the interactive lesson

Recap: First-Class Functions

You learned that in Python:

Functions are objects you can assign, store, pass, and return.
Higher-order functions take or return other functions (map, filter, sorted key).
lambda creates quick anonymous functions.
This enables clean dispatch tables instead of long conditionals.

ops = {'double': lambda x: x * 2}
print(ops['double'](21))

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Frequently Asked Questions

Is the “First-Class Functions” lesson free?

Yes — the full text of “First-Class Functions” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Python Academy course, upgrade to CoddyKit PRO. The Python Academy course includes 4 lessons in total.

What will I learn in “First-Class Functions”?

Pass and return functions. You practise Python Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Python Academy?

No prior experience is required. Python Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “First-Class Functions” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Python Academy lesson?

Yes. Every Python Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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