"In this example we have defined a parent class, Device, which
has attributes, and some child classes which contain their
particular attributes. We have created a list of instances of the
devices. In the "for loop" we do something only if the device has
the attribute getEths. Therefore we are using internal information
about the program, i.e. its classes, to control the program's
"By the way, this is sometimes referred to as "duck typing". If
it looks like a duck it must be a duck, therefore you can treat it
as a duck.
"Before proceeding, we should note that the Python language has
much similarity to a Python program, in that, everything in the
language is an object. For now we will limit the discussion to
classes and instances of classes. Just remember that Python has
many built in classes, there are hundreds in the "standard"
libraries,and many thousands which can be downloaded and all of the
classes themselves share some common properties."