Python Morsels: Python's "functions" are sometimes classes

Table of contents

1. Class or function?
2. What's a callable?
3. Classes are callables
4. Disguising classes as functions
5. Callable objects
6. The distinction between functions and classes often doesn't matter
7. Think in terms of "callables" not "classes" or "functions"

Class or function?

There's a group activity I often do when training new Python developers: the class or function game.

In the class or function game, we take something that we "call" (using parentheses: ()) and we guess whether it's a class or a function.

For example:

• We can call zip with a couple iterables and we get another iterable back, so is zip a class or a function?
• When we call len, are we calling a class or a function?
• What about int: when we write int('4') are we calling a class or a function?

Python's zip, len, and int are all often guessed to be functions, but only one of these is really a function:

>>> zip<class 'zip'>>>> len<built-in function len>>>> int<class 'int'>

>>> zip<class 'zip'>>>> len<built-in function len>>>> int<class 'int'>

While len is a function, zip and int are classes.

The reversed, enumerate, range, and filter"functions" also aren't really functions:

>>> reversed<class 'reversed'>>>> enumerate<class 'enumerate'>>>> range<class 'range'>>>> filter<class 'filter'>

>>> reversed<class 'reversed'>>>> enumerate<class 'enumerate'>>>> range<class 'range'>>>> filter<class 'filter'>

After the class or function game, we often talk discuss:

• The term "callable" (and how classes are callables)
• The fact that in Python we often don't care whether something is a class or a function

What's a callable?

A callable is anything you …