Author Dusty Phillips Reviewers

Method Resolution Order
) attribute on 
the class. This is beyond the scope of this book. If you think you need 
to understand it, I recommend 
Expert Python Programming
, 
Tarek Ziadé
, 
Packt Publishing
, or read the original documentation on the topic at 
http://www.python.org/download/releases/2.3/mro/
.
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Chapter 3
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 69 
]
Let's look at a second contrived example that illustrates this problem more clearly. 
Here we have a base class that has a method named 
call_me
. Two subclasses 
override that method, and then another subclass extends both of these using multiple 
inheritance. This is called diamond inheritance because of the diamond shape of the 
class diagram:
Subclass
BaseClass
+call_me()
LeftSubclass
RightSubclass
+call_me()
+call_me()
+call_me()
Let's convert this diagram to code; this example shows when the methods are called:
class BaseClass:
num_base_calls = 0
def call_me(self):
print("Calling method on Base Class")
self.num_base_calls += 1
class LeftSubclass(BaseClass):
num_left_calls = 0
def call_me(self):
BaseClass.call_me(self)
print("Calling method on Left Subclass")
self.num_left_calls += 1
class RightSubclass(BaseClass):
num_right_calls = 0
def call_me(self):
BaseClass.call_me(self)
print("Calling method on Right Subclass")
self.num_right_calls += 1
class Subclass(LeftSubclass, RightSubclass):
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When Objects Are Alike
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 70