MINOR: test for membership should be 'not in'
DOC: fix docstring position.
MINOR: fix 'x == False' comparison.
MINOR: Fix 'if not x is...'.
MINOR: use new-style classes
MINOR: remove unused import.
MINOR: fix comments.
MINOR: check for iterables against collections.Iterable
MINOR: check for ndarrays against np.ndarray