[Edu-sig] Getting ready for class...

[Gregor Lingl]

kirby urner schrieb:
> Here's what I'm starting with today:
> 
> http://www.4dsolutions.net/ocn/python/zoo.py
> 
> Note:  inheriting from object at the top level, per André's suggestion.
> 
> Kirby
> 

I also like this example very much (especially the somewhat 
sophisticated use of __repr__).

Despite of the lack of echo to my former (turtle-)example I'd like to 
contribute one more - this one without turtles (the English translation 
may be a bit inept):

In my class I let the students do the following exercise to sum up or 
recapitulate what they have learned in previous lessons about objects, 
inheritance and message passing:

We begin very simply (who wants may inherit from object):

 >>> class Messenger:
     def announce(self):
         print "I announce to you:", "Hello!"


 >>> herold = Messenger()
 >>> herold.announce()
I announce to you: Hello!
 >>> annunciator = Messenger()
 >>> annunciator.announce()
I announce to you: Hello!
 >>>

#### Not very diversified ... We improve it:

 >>> class Messenger:
     def announce(self, text):
         print "I announce to you:", text


 >>> herold = Messenger()
 >>> herold.announce("Fire on the roof")
I announce to you: Fire on the roof
 >>> herold.announce("Hurricane approaching!")
I announce to you: Hurricane approaching!
 >>>

#### Now we want the messengers to remember their message text:

 >>> class CleverMessenger:
     def note(self, text):
         self.message = text
     def announce(self):
         print "I announce to you:", self.message


 >>> wiseguy = CleverMessenger()
 >>> wiseguy.note("Shares are rising!")
 >>> wiseguy.announce()
I announce to you: Shares are rising!
 >>> vifzac = CleverMessenger()
 >>> vifzac.note("Weather is becoming cold!")
 >>> vifzac.announce()
I announce to you: Weather is becoming cold!
 >>>
 >>> vifzac.note("Weather is becoming warm!")
 >>> vifzac.announce()
I announce to you: Weather is becoming warm!
 >>> vifzac.message
'Weather is becoming warm!'

#### ( A look at an attribute )

#### Now inheritance: A VeryCleverMessenger 'isa' CleverMessenger

 >>> class VeryCleverMessenger(CleverMessenger):
     def note_additionally(self, addendum):
         self.message = self.message+" "+addendum

 >>> angelo = VeryCleverMessenger()
 >>> angelo.note("It's becoming cold!")
 >>> angelo.announce()
I announce to you: It's becoming cold!
 >>> angelo.note_additionally("Use warm clothing!")
 >>> angelo.announce()
I announce to you: It's becoming cold! Use warm clothing!
 >>> merkur = CleverMessenger()
 >>> merkur.note("Traffic jam on all Highways!")
 >>> merkur.note_additionally("Defer trip!")

Traceback (most recent call last):
   File "<pyshell#44>", line 1, in -toplevel-
     merkur.note_additionally("Defer trip!")
AttributeError: CleverMessenger instance has no attribute 
'note_additionally'

#### We see: merkur is not very clever

#### The following shows a serious defect of our messenger classes

 >>> zweistein = VeryCleverMessenger()
 >>> zweistein.announce()
I announce to you:

Traceback (most recent call last):
   File "<pyshell#46>", line 1, in -toplevel-
     zweistein.announce()
   File "<pyshell#20>", line 5, in announce
     print "I announce to you:", self.message
AttributeError: VeryCleverMessenger instance has no attribute 'message'

#### We will repair this by initializing the message attribute:

 >>> class CleverMessenger:
     def __init__(self):
         self.message="Hi!"
     def note(self, text):
         self.message = text
     def announce(self):
         print "I announce to you:", self.message


 >>> class VeryCleverMessenger(CleverMessenger):
     def note_additionally(self, addendum):
         self.message = self.message+" "+addendum

 >>> zweistein = VeryCleverMessenger()
 >>> zweistein.announce()
I announce to you: Hi!

#### One more inheritance example:

 >>> class FriendlyMessenger(CleverMessenger):
     def __init__(self, greeting):
         CleverMessenger.__init__(self)
         self.greeting = greeting
     def greet(self):
         print self.greeting

 >>> sunny = FriendlyMessenger("Have a nice day!")
 >>> sunny.greet()
Have a nice day!
 >>> sunny.announce()
I announce to you: Hi!

#### Overwrite methods

 >>> class FriendlyMessenger(CleverMessenger):
     def __init__(self, greeting):
         CleverMessenger.__init__(self)
         self.greeting = greeting
     def greet(self):
         print self.greeting
     def announce(self):
         self.greet()
         CleverMessenger.announce(self)

 >>> sunny = FriendlyMessenger("Have a nice day!")
 >>> sunny.announce()
Have a nice day!
I announce to you: Hi!
 >>> sunny.note("OOP is pretty useful!")
 >>> sunny.announce()
Have a nice day!
I announce to you: OOP is pretty useful!
 >>> tim = CleverMessenger()
 >>> tim.note("Tomorrow it will happen!")
 >>> tim.announce()
I announce to you: Tomorrow it will happen!

#### Last example: communicating objects

 >>> class Agent(CleverMessenger):
     def passMessage(self, agent):
         agent.note(self.message)
     def listen(self, agent):
         self.note(agent.message)

 >>> james = Agent()
 >>> austin = Agent()
 >>> james.announce()
I announce to you: Hi!
 >>> james.listen(tim)
 >>> james.announce()
I announce to you: Tomorrow it will happen!
 >>> austin.announce()
I announce to you: Hi!
 >>> james.passMessage(austin)
 >>> austin.announce()
I announce to you: Tomorrow it will happen!
 >>>

I assume that this interactive session is somewhat selfexplanatory, so I 
omit additional explanations.

Regards,
Gregor