flock_size—Indicates the number of birds seen in one sighting.(Remember that this is an overly simplified example. A real barn swallow would have many more
data attributes.)
These specialized data attributes are set using the following Python statements.
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self.__migratory = 'yes'
self.__flock_size = flock_sizeSince the first data attribute for the BarnSwallow subclass is immutable, the only mutator method
needed is for flock_size. This is set as follows:
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def set_flock_size(self,flock_size):
self.__flock_size = flock_sizeFinally, in the BarnSwallow subclass object definition, the accessor methods must be declared for
the subclass data attributes. They are shown here:
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def get_migratory(self):
return self.__migratory
def get_flock_size(self, flock_size):
return self.__flock_sizeOnce all the parts of the object definition have been determined, you can add the subclass to an object
module file.
Adding a Subclass to an Object Module File
The BarnSwallow subclass object definition can be stored in the same module file as the Bird
base class (see Listing 15.2).
LISTING 15.2 The BarnSwallow Subclass in the Bird Object File
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1: pi@raspberrypi ~ $ cat /home/pi/py3prog/birds.py
2: # Bird base class
3: #
4: class Bird:
5: #Initialize Bird class data attributes
6: def __init__(self, sex):
7: ...
8: #
9: # Barn Swallow subclass (base class: Bird)
10: #
11: class BarnSwallow(Bird):
12:
13: #Initialize Barn Swallow data attributes & obtain Bird inheritance.
14: def __init__(self, sex, flock_size):
15:
16: #Obtain base class data attributes & methods (inheritance)
17: Bird.__init__(self, sex)
18: