[Edu-sig] Introducing classes

[Andre Roberge]

A long time ago, Kirby suggested to me (on this list I believe - I
can't trace the post right now) that perhaps I should use rur-ple's
code itself as an example to use.  I replied that it was most likely
too complicated .... but I kept his idea at the back of my mind. 
After seeing his post on the Monkey class, I thought of how I would go
about to introduce classes, to users of rur-ple that have already
written simple programs to make a robot (Reeborg) move in his world,
both using the "function" notation and the OOP notation.

Here are my thoughts at the moment.  (Sorry for the amount of code; it
is designed to be all cut-and-pasted in one chunk to be run altogether
as an example.  In a classroom situation it would be broken up in
various steps.)  The next step would be to introduce the second
dimension (streets).

Any kind of comments would be appreciated, especially as I am thinking
of writing a rur-ple lesson using this approach :-)
André
====================

# Minimal robot that can move.

class Robot(object):
    def move(self):
        print "I moved."

Reeborg = Robot()
Reeborg.move()
print "----------------"

# Add real movement along a line
class Robot(object):
    def __init__(self):
        self.avenue = 1
    def move(self):
        self.avenue += 1
        print "I moved to Avenue %d"%self.avenue

Reeborg = Robot()
Reeborg.move()
Reeborg.move()
print "----------------"

# Add movement in both directions along the line
class Robot(object):
    def __init__(self):
        self.avenue = 1
        self.step = 1
    def move(self):
        self.avenue += self.step
        print "I moved to Avenue %d"%self.avenue
    def turn_around(self):
        self.step = -self.step
        print "I turned around."

Reeborg = Robot()
Reeborg.move()
Reeborg.move()
Reeborg.turn_around()
Reeborg.move()
print "----------------"

# Add obstacles (walls)
class Robot(object):
    def __init__(self):
        self.avenue = 1
        self.step = 1
        self.walls = [0, 5]
    def move(self):
        self.avenue += self.step
        if self.avenue in self.walls:
            print "A wall is preventing me to move to Avenue %d"%self.avenue
            self.avenue -= self.step
        else:
            print "I moved to Avenue %d"%self.avenue
    def turn_around(self):
        self.step = -self.step
        print "I turned around."

Reeborg = Robot()
Reeborg.move()
Reeborg.move()
Reeborg.turn_around()
Reeborg.move()
Reeborg.move()
Reeborg.move()
Reeborg.turn_around()
for i in range(5):
    Reeborg.move()
print "----------------"

# Create world and robot separately; put robot in world
class World(object):
    def __init__(self):
        self.walls = []
    def add_wall(self, avenue):
        self.walls.append(avenue)
    def is_clear(self, avenue):
        return avenue in self.walls

class Robot(object):
    def __init__(self, world):
        self.avenue = 1
        self.step = 1
        self.world = world
    def move(self):
        self.avenue += self.step
        if self.world.is_clear(self.avenue):
            print "Something in the world is preventing me",
            print "to move to Avenue %d"%self.avenue
            self.avenue -= self.step
        else:
            print "I moved to Avenue %d"%self.avenue
    def turn_around(self):
        self.step = -self.step
        print "I turned around."

w = World()
w.add_wall(0)
w.add_wall(5)
Reeborg = Robot(w)
Reeborg.move()
Reeborg.move()
Reeborg.move()
Reeborg.turn_around()
Reeborg.move()
Reeborg.move()
Reeborg.move()
Reeborg.move()
w.add_wall(3)
Reeborg.turn_around()
for i in range(3):
    Reeborg.move()
print "----------------"