Python’s empty function does not require a pass statement? [closed]

Question

I stumbled upon an interesting and unexpected feature of Python:

def fun():
    """Foo’s docstring"""

is a valid function? According to PEP 257, “A docstring is a string literal that occurs as the first statement in a module, function, class, or method definition” meaning that the docstring itself is considered a statement?

I would have expected that at least a pass statement is required here. The above example contradicts the Python Zen of “explicit is better than implicit” as pass states an explicit intent, and a docstring does not.

Can anybody shed some light on the intent?

Answer 1

A string literal is just like any other literal. It also works if you just put in an integer:

def func():
    1

However, it doesn't work if you only use a comment:

def func():
    # test

# IndentationError: expected an indented block

Even though it's also added as docstring (saved in the __doc__ attribute) it's also a function level constant:

def func():
    """I'm a function"""

>>> func.__code__.co_consts
("I'm a function", None)

So the presence of a string literal as only content of a function doesn't change how the function is actually "parsed" and "compiled" itself. Well, apart from the fact that it also got a not-None __doc__ attribute.

It's actually very handy for abstractmethods (see for example "Body of abstract method in Python"), where you don't need an actual function body.