index.lxp@lxpwrap=x2377_252ehtm.htm
来自「GUI Programming with Python」· HTM 代码 · 共 251 行
HTM
251 行
<table border="0" cellspacing="0" cellpadding="3" width="100%"><tr><td> <div align="center" id="bldcontent"> <a href="../default.htm"><img src="../images/opendocs.png" width="63" height="76" border="0"></a> <br> <div class="symbol">Your OpenSource Publisher™</div> </div> </td></tr></table> <div align="center" class="author"> <a href="../products.lxp">Products</a> | <a href="../wheretobuy.lxp">Where to buy</a> | <a href="../bookstore.lxp">Retailers</a> | <a href="../faq.lxp">FAQ</a> | <a href="../writeforus.lxp">Write for Us.</a> | <a href="#contact">Contact Us.</a> </div> <table border="0" cellspacing="3" cellpadding="0" width="100%"><tr><td width="100%"> <div class="content"> <table border="0" cellspacing="2" cellpadding="0" width="100%"><tr><td width="100%"> <div align="center"><H4 CLASS="AUTHOR"><A NAME="AEN5">Boudewijn Rempt</A><br><a href="../../https@secure.linuxports.com/opendocs/default.htm"><img src=odpyqt125.png></a><br>ISBN: 0-97003300-4-4<br><a href="../../https@secure.linuxports.com/opendocs/default.htm">Available from bookstores everywhere or you can order it here.</a><p>You can download the source files for the book <a href="pyqtsrc.tgz">(code / eps) here.</a><hr></div> <HTML><HEAD><TITLE>Circular references</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.72"><LINKREL="HOME"TITLE="GUI Programming with Python: QT Edition"HREF="book1.htm"><LINKREL="UP"TITLE="Python Objects and Qt Objects"HREF="c2341.htm"><LINKREL="PREVIOUS"TITLE="Python Objects and Qt Objects"HREF="c2341.htm"><LINKREL="NEXT"TITLE="Qt objects, Python objects and shadow objects"HREF="x2393.htm"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#0000FF"VLINK="#840084"ALINK="#0000FF"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">GUI Programming with Python: QT Edition</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><A accesskey="P" href="index.lxp@lxpwrap=c2341_252ehtm.htm">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 9. Python Objects and Qt Objects</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><A accesskey="N" href="index.lxp@lxpwrap=x2393_252ehtm.htm">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1">Circular references</A></H1><P>You can cause a memory leak in Python by creating circular references, or by never deleting the last reference to an object. The latest versions of Python support a garbage collector that can detect circular references and clean them up. It's quite difficult to create circular references, but it's very easy to accidentally keep references lying about. The next snippet shows the circularity of referring from A to B to A... </P><DIVCLASS="EXAMPLE"></A><P><B>Example 9-2. circular.py - circululululular references</B></P><PRECLASS="PROGRAMLISTING">## circular.py - circululululular references in Python#class B: passclass A: def __init__(self): self.b=B() self.b.a=selfa=A()print aprint a.bprint a.b.aprint a.b.a.b.a.b.a.b.a.b.a.b.a.b.a.b.a.b.a.b.a.b.a </PRE></DIV><PRECLASS="SCREEN">boudewijn@maldar:~/doc/opendoc/ch3 > python circular.py<__main__.A instance at 0x8199bb4><__main__.B instance at 0x8199c04><__main__.A instance at 0x8199bb4><__main__.A instance at 0x8199bb4> </PRE><P>If you delete the instance <TTCLASS="VARNAME">a</TT>, you only make the objects inaccessible; because <TTCLASS="VARNAME">b</TT> still refers to <TTCLASS="VARNAME">a</TT>, there's a reference for the reference counter, and <TTCLASS="VARNAME">a</TT> will not be destroyed. Thus <TTCLASS="VARNAME">b</TT> will not be destroyed either, which means the reference to <TTCLASS="VARNAME">a</TT> remains in existence — ad infinitum! (Or at least until the Python interpreter shuts down.)</P></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><A accesskey="P" href="index.lxp@lxpwrap=c2341_252ehtm.htm">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><A accesskey="H" href="index.lxp@lxpwrap=book1_252ehtm">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><A accesskey="N" href="index.lxp@lxpwrap=x2393_252ehtm.htm">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Python Objects and Qt Objects</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><A accesskey="U" href="index.lxp@lxpwrap=c2341_252ehtm.htm">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Qt objects, Python objects and shadow objects</TD></TR></TABLE></DIV></BODY></HTML> </td> </tr> </table> </td> </tr> </table> ⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?