non-data descriptor __getattribute__ breaks the descriptor usage use more than one instance for testing examples conclusion more examples generalized attribute validation function decorators @property descriptors generalized validation summary inheritance with super super child before parent inherit __init__ inherit __init__ of multiple classes math problem conclusion generators feed iterations receive values send and receive values return values in generator 'yield fromcommand unix commands introduction 'argparse find command details python implementation grep cat caffe installation in ubuntu prerequisite install packages create virtualenv install virtualenv modify bashrc create virtualenv install opencv install caffe index