Why naked Python decorators (without @) do not generate compiler error?

Question

Just a mistype: I forgot to add @ before property decorator. Lost approx 1 hour to find out what went wrong. Here is an example:

class Woo(object):
    @property
    def success(self):
        return True

    property
    def failure(self):
        return False

if __name__ == '__main__':
    woo = Woo()
    print(f'success={woo.success}')
    print(f'failure={woo.failure}')
    print(f'It\'s fine to call failure()={woo.failure()}')

The result is:

success=True
failure=<bound method Woo.failure of <__main__.Woo object at 0x0000016050D4F6D8>>
It's fine to call failure()=False

I'm wondering why Python compiler allows "naked decorator" (e.g. property without decorator prefix @) in syntax and what does it mean semantically.

Answer 1

It's perfectly legal to have a symbol floating around without any purpose, similar to this:

a = 1
a  # Perfectly legal, although a thorough linter* will cause a warning

In your example, it's just a top-level reference to the property class that isn't used for anything, similar to if you had:

class MyClass:
    a = 1

    a  # Legal, but causes a warning since it has no purpose
    def meth(self):
        pass

    1  # Also legal but useless
    def another_meth(self):
        pass

It isn't being treated as a decorator; it's being treated as a plain reference to the property class in a context where it isn't used for anything.

---

* Pycharm gives the warning Statement seems to have no effect.