Better support for PEP 526 instance and classvar annotations

[belm0]

Steps to reproduce

A class which doesn't have __init__ (it may set attributes in __new__, for example) will yield no-member when instance attributes are accessed.

I tried to resolve it with PEP 526 instance var annotations which don't have assignment (i.e. type only), but still get no-member error.

class Foo:
    bar:  int
    ...

x = Foo()
x.bar

Current behavior

E1101: Instance of 'Foo' has no 'bar' member (no-member)

Expected behavior

no warnings

pylint --version output

pylint 2.3.1
astroid 2.3.0
Python 3.7.0b3 (default, Aug 25 2018, 16:41:39)
[Clang 9.0.0 (clang-900.0.39.2)]

[PCManticore]

The check is correct, that annotation is not accessible as an attribute in Python. You'll most likely get an error as the following if you attempt to run the code:

Traceback (most recent call last):
  File "a.py", line 6, in <module>
    x.bar
AttributeError: 'Foo' object has no attribute 'bar'

[belm0]

@PCManticore please let me clarify with a complete example:

class Foo(BaseException):
    bar:  int

    def __new__(cls):
        o = BaseException.__new__(cls)
        o.bar = 10
        return o

x = Foo()
print(x.bar)

E1101: Instance of 'Foo' has no 'bar' member (no-member)

From my understanding of PEP 526, one of the points is to enable typing in complex initialization scenarios.

I'll note that if Foo simply derives from object, then pylint does not emit the error, even if the annotation is removed. So it seems this has something to do with type derivation.

[PCManticore]

Ah, thanks, I definitely misunderstood the purpose of the PEP.