oop.py (plain text)

"""Implementing OOP"""

def make_instance(cls):
    """Return a new object instance."""

    def get_value(name):
        if name in attributes:
            return attributes[name]
        else:
            value = cls['get'](name)
            return bind_method(value, instance)
    
    def set_value(name, value):
        attributes[name] = value
    
    attributes = {}
    instance = {'get': get_value, 'set': set_value}
    return instance


def bind_method(value, instance):
    """Return value or a bound method if value is callable."""
    if callable(value):
        def method(*args):
            return value(instance, *args)
        return method
    else:
        return value


def make_class(attributes, base_class=None):
    """Return a new class.
    
    attributes -- class attributes
    base_class -- a dispatch dictionary representing a class
    """

    def get_value(name):
        if name in attributes:
            return attributes[name]
        elif base_class is not None:
            return base_class['get'](name)

    def set_value(name, value):
        attributes[name] = value

    def new(*args):
        return init_instance(cls, *args)

    cls = {'get': get_value, 'set': set_value, 'new': new}
    return cls


def init_instance(cls, *args):
    """Return a new instance of cls, initialized with args."""
    instance = make_instance(cls)
    init = cls['get']('__init__')
    if init is not None:
        init(instance, *args)
    return instance