Avoid warning in Gateway.__del__

[TomAugspurger]

This test was emitting a warning, which came from garbage collection on
Gateway objects that failed in __init__.

E               Traceback (most recent call last):
E                 File "/home/taugspurger/src/dask/dask-gateway/dask-gateway/dask_gateway/client.py", line 376, in __del__
E                   not self.asynchronous
E                 File "/home/taugspurger/src/dask/dask-gateway/dask-gateway/dask_gateway/client.py", line 334, in asynchronous
E                   return self._asynchronous
E               AttributeError: 'Gateway' object has no attribute '_asynchronous'

[jcrist]

Thanks Tom!

[jcrist]

In case the property changes implementation, should maybe check the referenced name instead of an implementation detail.

Suggested change

	if hasattr(self, "_asynchronous") and (
	if hasattr(self, "asynchronous") and (

[TomAugspurger]

Let me check that. I assumed hasattr always returned true for properties, but maybe not if they raise an AttributeError?

[TomAugspurger]

OK switched to use asynchronous and there's no warning, but I have no idea why it's working. It seems like hasattr does always evaluate true in this case:

In [1]: class Foo:
   ...:     @property
   ...:     def a(self):
   ...:         return self._a
   ...:

In [2]: hasattr(Foo, "a")
Out[2]: True

so I would expect the warning to be back when using the property name. But I guess it doesn't really matter, as long as it works.

[jcrist]

You're checking on the class above (which will always work), when what you meant to do was check on an instance

>>> hasattr(Foo, "a")
True
>>> hasattr(Foo(), "a")
False

hasattr is basically:

def hasattr(x, name):
    try:
        getattr(x, name)
        return True
    except AttributeError:
        return False

[jcrist]

Test failure is a known CI issue. Merging, thanks Tom!