📄 page119.html
字号:
<HTML><HEAD><TITLE>Container __init__, hookiterand purge methods</TITLE></HEAD><BODY bgcolor="#FFFFFF"> <a href="../index.html" target="_top"><img src="../icons/usins.gif" alt="Logo" align=right></a><b>Data Structures and Algorithms with Object-Oriented Design Patterns in Python</b><br><A NAME="tex2html2586" HREF="page120.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="../icons/next_motif.gif"></A> <A NAME="tex2html2584" HREF="page118.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="../icons/up_motif.gif"></A> <A NAME="tex2html2578" HREF="page118.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="../icons/previous_motif.gif"></A> <A NAME="tex2html2588" HREF="page611.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="../icons/index_motif.gif"></A> <BR><HR><H3><A NAME="SECTION005231000000000000000"><tt>Container</tt> <tt>__init__</tt>, hookiterand <tt>purge</tt> methods</A></H3><P>A container may be empty or it may contain one or more other objects.Typically, a container has finite capacity.As shown in Program <A HREF="page119.html#progcontainera"><IMG ALIGN=BOTTOM ALT="gif" SRC="../icons/cross_ref_motif.gif"></A>,a single instance attribute called <tt>_count</tt>is used to keep track of the number of objects held in the container.The <tt>_count</tt> instance attribute is set initially to zero.It is the responsibility of the derived classto update this instance attribute as required.<P><P><A NAME="4948"> </A><A NAME="progcontainera"> </A> <IMG WIDTH=575 HEIGHT=294 ALIGN=BOTTOM ALT="program4516" SRC="img647.gif" ><BR><STRONG>Program:</STRONG> <tt>Container</tt> class.<BR><P><P>The purpose of the <tt>purge</tt> method is to discardall of the contents of a container.This method is declared abstract becausethe manner in which the <tt>purge</tt> method is implementeddepends on the type of the container.After a container is purged,the value of the <tt>_count</tt> instance attribute should be zero.<P>The purpose of the <tt>__iter__</tt> method is to returnan iterator that enumerates the objects in the container.Iterators are discussed in Section <A HREF="page121.html#secadtsiterators"><IMG ALIGN=BOTTOM ALT="gif" SRC="../icons/cross_ref_motif.gif"></A>.<P><HR><A NAME="tex2html2586" HREF="page120.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="../icons/next_motif.gif"></A> <A NAME="tex2html2584" HREF="page118.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="../icons/up_motif.gif"></A> <A NAME="tex2html2578" HREF="page118.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="../icons/previous_motif.gif"></A> <A NAME="tex2html2588" HREF="page611.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="../icons/index_motif.gif"></A> <P><ADDRESS><img src="../icons/bruno.gif" alt="Bruno" align=right><a href="../copyright.html">Copyright © 2003</a> by <a href="../signature.html">Bruno R. Preiss, P.Eng.</a> All rights reserved.</ADDRESS></BODY></HTML>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -