> This is something that one can only gain from experience?
> I really had to struggle to get the Light class to work at all.
> I have no idea how many times I started over. But I do feel
> that I am starting to learn some of this stuff.
This surprises me... I guess it does take experience. What is the most basic
thing you can describe about a light? Immediately I answer, "You can turn it
on or off". This suggests methods, turn_on(), turn_off(), and something to
maintain the state of the light attribute - i.e. whether it is currently on
or not. I suggest practice practice practice. You should be able to look at
anything in your house and be able to design a basic class for it. Some that
come to mind as I look around the room. I've often thought of redesigning my
entire house in OOP. ;-)
(Granted - these examples aren't entirely useful, but they provide examples
of practice with methods and attributes.)
class Pen:
def __init__(self):
self.level = 50
self.on = False
def click(self):
self.on = (not self.on)
def isempty(self):
return (self.level > 0)
def write(self):
if self.isempty:
return False
if not self.on:
return False
self.level = self.level - 5
return True
class Knob:
def __init__(self, locked=False):
self.locked = locked
def turn(self):
if self.locked:
return False
return True
class Door:
def __init__(self):
self.knob = Knob()
def lock(self):
self.knob.locked = True
def unlock(self):
self.knob.locked = False
def open(self):
return self.knob.turn()
Are some simple examples off the top of my head. It's not difficult to model
real-life things with classes, but it is much more difficult to model them
in such a way that you interact with them normally. (i.e. do you lock the
door, or the knob? Does the knob contain a Lock, or does the developer only
need to know that it has one and whether it is locked or not?)
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