Error
Traceback (most recent call last):
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 245, in _as_instance
    inst = class_.__dict__[self.key + "_inst"]
KeyError: '_AssociationProxy__columns_4746492392_inst'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.6.4_4/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/usr/local/Cellar/python/3.6.4_4/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/case.py", line 601, in run
    self.setUp()
  File "/Users/luke/Documents/Projects/my-project/tests/reports.py", line 49, in setUp
    ['3/1/18', 5, 6]
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 202, in __set__
    return self._as_instance(class_, obj).set(obj, values)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 567, in set
    proxy._bulk_replace(self, values)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 967, in _bulk_replace
    assoc_proxy._set(self, values)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 631, in _set
    proxy.extend(values)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 1067, in extend
    self.append(v)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 1052, in append
    item = self._create(value)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 974, in _create
    return self.creator(value)
  File "<string>", line 4, in __init__
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/orm/state.py", line 441, in _initialize_instance
    manager.dispatch.init_failure(self, args, kwargs)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 129, in reraise
    raise value
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/orm/state.py", line 438, in _initialize_instance
    return manager.original_init(*mixed[1:], **kwargs)
  File "/Users/luke/Documents/Projects/my-project/my/project/models/datatablerow.py", line 16, in __init__
    self._proxied = values
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 202, in __set__
    return self._as_instance(class_, obj).set(obj, values)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 249, in _as_instance
    inst = AssociationProxyInstance.for_proxy(self, owner, obj)
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 375, in for_proxy
    target_assoc, parent, owning_class, target_class, value_attr
  File "/Users/luke/Documents/Projects/my-project/venv/lib/python3.6/site-packages/sqlalchemy/ext/associationproxy.py", line 388, in _construct_for_assoc
    if attr._is_internal_proxy and not hasattr(attr, "impl"):
AttributeError: 'property' object has no attribute '_is_internal_proxy'