This may also occur if your using slots in class and have not added this new attribute in slots yet.
class xyz(object):
"""
class description
"""
__slots__ = ['abc', 'ijk']
def __init__(self):
self.abc = 1
self.ijk = 2
self.pqr = 6 # This will throw error 'AttributeError: object has no attribute 'pqr'
