Is it possible to have static type declarations for function input arguments in Python3.7?

Question

This is a syntax I see in Python3 code skeletons on leetcode.com. Note the type declarations of the function input arguments (or at least I think they're type declarations, never seen it before). nums must be a List of int, and s must be an int.

class Solution:
    def findTargetSumWays(self, nums: List[int], S: int) -> int:
        pass

If I run that function inside the environment on leetcode.com, it exits without error. However, if I run the same code in my own Python 3.7.3 environment, I get a NameError.

def findTargetSumWays(self, nums: List[int], S: int) -> int: NameError: name 'List' is not defined

What is wrong? Is the syntax on leetcode.com even real Python?

The technical term is *function annotation*, one use (and the only officially supported use) of which is for type hints. — chepner, May 02 '19 at 13:41

score 1 · Accepted Answer · answered May 02 '19 at 13:41

1

Yes, this is real syntax, officially used since 3.7 I believe.

The List used in this static typing is imported from the typing module.

You can read more about it in PEP-484: Type Hints or in the typing module docs.

answered May 02 '19 at 13:41

Faboor

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Ah! Invisible imports on leetcode.com had me fooled. – Magnus May 02 '19 at 13:45

Is it possible to have static type declarations for function input arguments in Python3.7?

1 Answers1