Python3/en: multiple inheritance (#2217)

* Add __name__ check to make testing easier

* Update say to call print. Add more usage examples

* Move Modules section before Classes

Makes more sense for when explaining inheritance

* Add multiple inheritance example

* Add examples for multiple inheritance

* Add instance check examples

* Fix multiple inheritance example

* Add note on the __name__ variable

1 files changed, 147 insertions, 50 deletions

diff --git a/python3.html.markdown b/python3.html.markdown
index 0f5da8f1..7f3702e6 100644
--- a/python3.html.markdown
+++ b/python3.html.markdown
@@ -601,10 +601,47 @@ list(filter(lambda x: x > 5, [3, 4, 5, 6, 7]))  # => [6, 7]
 [add_10(i) for i in [1, 2, 3]]         # => [11, 12, 13]
 [x for x in [3, 4, 5, 6, 7] if x > 5]  # => [6, 7]
 
+
 ####################################################
-## 5. Classes
+## 5. Modules
 ####################################################
 
+# You can import modules
+import math
+print(math.sqrt(16))  # => 4.0
+
+# You can get specific functions from a module
+from math import ceil, floor
+print(ceil(3.7))   # => 4.0
+print(floor(3.7))  # => 3.0
+
+# You can import all functions from a module.
+# Warning: this is not recommended
+from math import *
+
+# You can shorten module names
+import math as m
+math.sqrt(16) == m.sqrt(16)  # => True
+
+# Python modules are just ordinary python files. You
+# can write your own, and import them. The name of the
+# module is the same as the name of the file.
+
+# You can find out which functions and attributes
+# defines a module.
+import math
+dir(math)
+
+# If you have a Python script named math.py in the same
+# folder as your current script, the file math.py will
+# be loaded instead of the built-in Python module.
+# This happens because the local folder has priority
+# over Python's built-in libraries.
+
+
+####################################################
+## 6. Classes
+####################################################
 
 # We use the "class" operator to get a class
 class Human:
@@ -627,7 +664,11 @@ class Human:
 
     # An instance method. All methods take "self" as the first argument
     def say(self, msg):
-        return "{name}: {message}".format(name=self.name, message=msg)
+        print ("{name}: {message}".format(name=self.name, message=msg))
+
+    # Another instance method
+    def sing(self):
+        return 'yo... yo... microphone check... one two... one two...'
 
     # A class method is shared among all instances
     # They are called with the calling class as the first argument
@@ -658,71 +699,127 @@ class Human:
         del self._age
 
 
-# Instantiate a class
-i = Human(name="Ian")
-print(i.say("hi"))     # prints out "Ian: hi"
+# When a Python interpreter reads a source file it executes all its code.
+# This __name__ check makes sure this code block is only executed when this
+# module is the main program.
+if __name__ == '__main__':
+    # Instantiate a class
+    i = Human(name="Ian")
+    i.say("hi")                     # "Ian: hi"
+    j = Human("Joel")
+    j.say("hello")                  # "Joel: hello"
+    # i and j are instances of type Human, or in other words: they are Human objects
+
+    # Call our class method
+    i.say(i.get_species())          # "Ian: H. sapiens"
+    # Change the shared attribute
+    Human.species = "H. neanderthalensis"
+    i.say(i.get_species())          # => "Ian: H. neanderthalensis"
+    j.say(j.get_species())          # => "Joel: H. neanderthalensis"
+
+    # Call the static method
+    print(Human.grunt())            # => "*grunt*"
+    print(i.grunt())                # => "*grunt*"
+
+    # Update the property for this instance
+    i.age = 42
+    # Get the property
+    i.say(i.age)                    # => 42
+    j.say(j.age)                    # => 0
+    # Delete the property
+    del i.age
+    # i.age                         # => this would raise an AttributeError
 
-j = Human("Joel")
-print(j.say("hello"))  # prints out "Joel: hello"
 
-# Call our class method
-i.get_species()  # => "H. sapiens"
+####################################################
+## 6.1 Multiple Inheritance
+####################################################
 
-# Change the shared attribute
-Human.species = "H. neanderthalensis"
-i.get_species()  # => "H. neanderthalensis"
-j.get_species()  # => "H. neanderthalensis"
+# Another class definition
+class Bat:
 
-# Call the static method
-Human.grunt()    # => "*grunt*"
+    species = 'Baty'
 
-# Update the property
-i.age = 42
+    def __init__(self, can_fly=True):
+        self.fly = can_fly
 
-# Get the property
-i.age # => 42
+    # This class also has a say method
+    def say(self, msg):
+        msg = '... ... ...'
+        return msg
 
-# Delete the property
-del i.age
-i.age  # => raises an AttributeError
+    # And its own method as well
+    def sonar(self):
+        return '))) ... ((('
 
+if __name__ == '__main__':
+    b = Bat()
+    print(b.say('hello'))
+    print(b.fly)
 
 
-####################################################
-## 6. Modules
-####################################################
+# from "filename-without-extension" import "function-or-class"
+from human import Human
+from bat import Bat
 
-# You can import modules
-import math
-print(math.sqrt(16))  # => 4.0
+# Batman inherits from both Human and Bat
+class Batman(Human, Bat):
 
-# You can get specific functions from a module
-from math import ceil, floor
-print(ceil(3.7))   # => 4.0
-print(floor(3.7))  # => 3.0
+    # Batman has its own value for the species class attribute
+    species = 'Superhero'
 
-# You can import all functions from a module.
-# Warning: this is not recommended
-from math import *
+    def __init__(self, *args, **kwargs):
+        # Typically to inherit attributes you have to call super:
+        #super(Batman, self).__init__(*args, **kwargs)      
+        # However we are dealing with multiple inheritance here, and super()
+        # only works with the next base class in the MRO list.
+        # So instead we explicitly call __init__ for all ancestors.
+        # The use of *args and **kwargs allows for a clean way to pass arguments,
+        # with each parent "peeling a layer of the onion".
+        Human.__init__(self, 'anonymous', *args, **kwargs)
+        Bat.__init__(self, *args, can_fly=False, **kwargs)
+        # override the value for the name attribute
+        self.name = 'Sad Affleck'
 
-# You can shorten module names
-import math as m
-math.sqrt(16) == m.sqrt(16)  # => True
+    def sing(self):
+        return 'nan nan nan nan nan batman!'
 
-# Python modules are just ordinary python files. You
-# can write your own, and import them. The name of the
-# module is the same as the name of the file.
 
-# You can find out which functions and attributes
-# defines a module.
-import math
-dir(math)
+if __name__ == '__main__':
+    sup = Batman()
+
+    # Instance type checks
+    if isinstance(sup, Human):
+        print('I am human')
+    if isinstance(sup, Bat):
+        print('I am bat')
+    if type(sup) is Batman:
+        print('I am Batman')
+
+    # Get the Method Resolution search Order used by both getattr() and super().
+    # This attribute is dynamic and can be updated
+    print(Batman.__mro__)       # => (<class '__main__.Batman'>, <class 'human.Human'>, <class 'bat.Bat'>, <class 'object'>)
+
+    # Calls parent method but uses its own class attribute
+    print(sup.get_species())    # => Superhero
+
+    # Calls overloaded method
+    print(sup.sing())           # => nan nan nan nan nan batman!
+
+    # Calls method from Human, because inheritance order matters
+    sup.say('I agree')          # => Sad Affleck: I agree
+
+    # Call method that exists only in 2nd ancestor
+    print(sup.sonar())          # => ))) ... (((
+
+    # Inherited class attribute
+    sup.age = 100
+    print(sup.age)
+
+    # Inherited attribute from 2nd ancestor whose default value was overriden
+    print('Can I fly? ' + str(sup.fly))
+
 
-# If you have a Python script named math.py in the same
-# folder as your current script, the file math.py will
-# be loaded instead of the built-in Python module.
-# This happens because the local folder has priority
-# over Python's built-in libraries.
 
 ####################################################
 ## 7. Advanced