第6章：继承和抽象类

#!/usr/bin/env python

# -*- coding:utf-8 -*-

# Author:Lijunjie

"""

File: arraysortedbag.py

"""

from arraybag import ArrayBag

class ArraySortedBag( ArrayBag ):

    """An array-based sorted bag implementation."""

    #Constructor

    def __init__( self, sourceCollection = None ):

        """Sets the initial state of self, which includes the contents

        of sourceCollection, if it‘s present."""

        ArrayBag.__init__( self, sourceCollection )

    #Accessor method

    def __contains__( self, item ):

        """Return True if item is in self, or False otherwise"""

        left = 0

        right = len( self ) - 1

        while left <= right:

            midpoint = ( left + right ) // 2

            if self._items[midpoint] == item :

                return True

            if self._items[midpoint] > item :

                right = midpoint - 1

            else:

                left = midpoint + 1

        return False 

    #Mutator method

    def add( self, item ):

        """Adds item to self."""

        #Empty or last item, call ArrayBag.add

        if self.isEmpty() or item >= self._items[len( self ) - 1]:

            ArrayBag.add( self, item )

        else:

            #Resize the array if it is full here

            #Search for the first item > = new item

            targetIndex = 0

            while item > self._items[targetIndex]:

                targetIndex += 1

            #open a hole for a newitem

            for index in range( len( self ), targetIndex, -1 ):

                self._items[index] = self._items[index - 1]

            #insert item and update size

            self._items[targetIndex] = item

            self._size += 1 

"""

File: abstractbag.py

Author: Lijunjie

"""

class AbstractBag( object ):

    """An abstract bag implementation."""

    #Constructor

    def __init__( self, sourceCollection = None ):

        """Sets the initial state of self, which includes the contents

        of sourceCollection, if it‘s present."""

        self._size = 0

        if sourceCollection:

            for item in sourceCollection:

                self.add( item ) 

    def __add__( self, other ):

        """Return a new bag containing the contents of self and other"""

        result = type( self )( self )

        for item in other:

            result.add( item )

        return result 

    def __eq__( self, other ):

        """Return True if self equals other, otherwise False."""

        if self is other: return True

        if type( self ) != type( other ) or len( self ) != len( other ):

            return False

        otherIter = iter( other )

        for item in self:

            if item != next( otherIter ):

                return False

        return True