Mypy expects @property's to follow each other

[mchlnix]

• Are you reporting a bug, or opening a feature request?
  Bug
• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

class Works:
    def __init__(self):
        self._a = 0

    @property
    def a(self):
        return self._a

    @a.setter
    def a(self, value):
        self._a = value


class Doesnt:
    def __init__(self):
        self._a = 0

    @property
    def a(self):
        return self._a

    def another_method(self):
        print("This is unimportant")

    @a.setter
    def a(self, value):
        self._a = value

• What is the actual behavior/output?

test-mypy.py:25: error: Name 'a' already defined on line 18
test-mypy.py:25: error: "Callable[[Any], Any]" has no attribute "setter"

• What is the behavior/output you expect?
  That parts of a property definition do not have to follow each other directly to be recognized as such.
• What are the versions of mypy and Python you are using?
  Python: 3.6.5
  Mypy: 0.720
• Do you see the same issue after installing mypy from Git master?
  Yes
• What are the mypy flags you are using? (For example --strict-optional)
  None

[JukkaL]

Closing as duplicate of #1465.