What does '->' mean in a function declaration in Python 3?

Question

Recently, I have come across this -> in Python 3 when studying function declarations. What does this do and mean? I have never seen such a declaration other than in a Javascript function declaration up until now.

def f(self, s: 'str') -> 'bool':
    pass

Function f will return a boolean value. This enhances readability and makes it easy to debug. — taurus05
– taurus05, Commented Feb 6, 2019 at 5:59
Does this answer your question? What does -> mean in Python function definitions? — Gino Mempin
– Gino Mempin, Commented Oct 18, 2022 at 9:20

Sach · Accepted Answer · 2019-02-06 06:08:54Z

8

This is annotation for type of return value of function.

def sum() -> expression:

That is, the parameter list can now be followed by a literal -> and a Python expression. Like the annotations for parameters, this expression will be evaluated when the function definition is executed.

https://www.python.org/dev/peps/pep-3107/

answered Feb 6, 2019 at 6:08

Sach

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tbhaxor · Accepted Answer · 2019-02-06 06:05:31Z

3

According to python docs related to typings.

This is the python typing feature, which let you specify the return type of functions in python

answered Feb 6, 2019 at 6:05

tbhaxor

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