COP 3223H meeting -*- Outline -*-

* object-oriented classes background

   This is background for representing recursive data in Python,
   as in grammars and abstract syntax trees.

** classes define how objects are produced and behave
    This is a very simple class
    Classes produce objects like factories produce, say, sunglasses

    Point out each kind of method
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       PYTHON CLASSES DEFINE OBJECTS

class Cell(object):
    def __init__(self, value):
        """Initialize this cell with the given value."""


    def value(self):
        """Return the value in this cell."""


    def set(self, value):
        """Change the value in this cell to be the given value."""


    def __repr__(self):
        """Return a string representation of this cell."""


    def __str__(self):
        """Return a string showing the value in this cell."""


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        Note that object is the superclass of Cell,
             from which it inherits behavior
             Thus Cell is a subclass of object,
             and we also say that Cell is a subtype of object.
             
        ... self.val = value
        ... return self.val
        ... self.val = value
        ... return "Cell(" + repr(self.value()) + ")"
        ... return "Cell(" + str(self.value()) + ")"

        Point out that repr(o) calls o.__repr__()
        and str(o) calls o.__str__()

** object construction
------------------------------------------
           OBJECT CONSTRUCTION

Objects are constructed by calling
the class name as a function,




Example:

     c1 = Cell(1)
     c2 = Cell(2)
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    ... passing it the arguments from the __init__()
        method, other than self


** method calls
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             METHOD CALLS

Functions in a class that have a self argument
are called 

Method calls are written:

       e.m(args)




for example:

      c1.value()
      c2.set(3)
      
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        ... methods
        ... where the value of e is the receiver, passed as self
            and args are the other arguments of the method (not self)