projects / OpenSPARC-T2-DV / blame
| Commit | Line | Data |
|---|---|---|
| 86530b38 AT |
1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
| 2 | <html> | |
| 3 | <head> | |
| 4 | <link rel="STYLESHEET" href="ref.css" type='text/css' /> | |
| 5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> | |
| 6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> | |
| 7 | <link rel="first" href="ref.html" title='Python Reference Manual' /> | |
| 8 | <link rel='contents' href='contents.html' title="Contents" /> | |
| 9 | <link rel='index' href='genindex.html' title='Index' /> | |
| 10 | <link rel='last' href='about.html' title='About this document...' /> | |
| 11 | <link rel='help' href='about.html' title='About this document...' /> | |
| 12 | <link rel="next" href="metaclasses.html" /> | |
| 13 | <link rel="prev" href="customization.html" /> | |
| 14 | <link rel="parent" href="specialnames.html" /> | |
| 15 | <link rel="next" href="new-style-attribute-access.html" /> | |
| 16 | <meta name='aesop' content='information' /> | |
| 17 | <title>3.3.2 Customizing attribute access</title> | |
| 18 | </head> | |
| 19 | <body> | |
| 20 | <DIV CLASS="navigation"> | |
| 21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> | |
| 22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
| 23 | <tr> | |
| 24 | <td class='online-navigation'><a rel="prev" title="3.3.1 Basic customization" | |
| 25 | href="customization.html"><img src='../icons/previous.png' | |
| 26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 27 | <td class='online-navigation'><a rel="parent" title="3.3 Special method names" | |
| 28 | href="specialnames.html"><img src='../icons/up.png' | |
| 29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
| 30 | <td class='online-navigation'><a rel="next" title="3.3.2.1 More attribute access" | |
| 31 | href="new-style-attribute-access.html"><img src='../icons/next.png' | |
| 32 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
| 33 | <td align="center" width="100%">Python Reference Manual</td> | |
| 34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
| 35 | href="contents.html"><img src='../icons/contents.png' | |
| 36 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
| 37 | <td class='online-navigation'><img src='../icons/blank.png' | |
| 38 | border='0' height='32' alt='' width='32' /></td> | |
| 39 | <td class='online-navigation'><a rel="index" title="Index" | |
| 40 | href="genindex.html"><img src='../icons/index.png' | |
| 41 | border='0' height='32' alt='Index' width='32' /></A></td> | |
| 42 | </tr></table> | |
| 43 | <div class='online-navigation'> | |
| 44 | <b class="navlabel">Previous:</b> | |
| 45 | <a class="sectref" rel="prev" href="customization.html">3.3.1 Basic customization</A> | |
| 46 | <b class="navlabel">Up:</b> | |
| 47 | <a class="sectref" rel="parent" href="specialnames.html">3.3 Special method names</A> | |
| 48 | <b class="navlabel">Next:</b> | |
| 49 | <a class="sectref" rel="next" href="new-style-attribute-access.html">3.3.2.1 More attribute access</A> | |
| 50 | </div> | |
| 51 | <hr /></div> | |
| 52 | </DIV> | |
| 53 | <!--End of Navigation Panel--> | |
| 54 | ||
| 55 | <H2><A NAME="SECTION005320000000000000000"></A><A NAME="attribute-access"></A> | |
| 56 | <BR> | |
| 57 | 3.3.2 Customizing attribute access | |
| 58 | </H2> | |
| 59 | ||
| 60 | <P> | |
| 61 | The following methods can be defined to customize the meaning of | |
| 62 | attribute access (use of, assignment to, or deletion of <code>x.name</code>) | |
| 63 | for class instances. | |
| 64 | ||
| 65 | <P> | |
| 66 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 67 | <td><nobr><b><tt id='l2h-206' xml:id='l2h-206' class="method">__getattr__</tt></b>(</nobr></td> | |
| 68 | <td><var>self, name</var>)</td></tr></table></dt> | |
| 69 | <dd> | |
| 70 | Called when an attribute lookup has not found the attribute in the | |
| 71 | usual places (i.e. it is not an instance attribute nor is it found in | |
| 72 | the class tree for <code>self</code>). <code>name</code> is the attribute name. | |
| 73 | This method should return the (computed) attribute value or raise an | |
| 74 | <tt class="exception">AttributeError</tt> exception. | |
| 75 | ||
| 76 | <P> | |
| 77 | Note that if the attribute is found through the normal mechanism, | |
| 78 | <tt class="method">__getattr__()</tt> is not called. (This is an intentional | |
| 79 | asymmetry between <tt class="method">__getattr__()</tt> and <tt class="method">__setattr__()</tt>.) | |
| 80 | This is done both for efficiency reasons and because otherwise | |
| 81 | <tt class="method">__setattr__()</tt> would have no way to access other attributes of | |
| 82 | the instance. Note that at least for instance variables, you can fake | |
| 83 | total control by not inserting any values in the instance attribute | |
| 84 | dictionary (but instead inserting them in another object). See the | |
| 85 | <tt class="method">__getattribute__()</tt> method below for a way to actually get | |
| 86 | total control in new-style classes. | |
| 87 | <a id='l2h-208' xml:id='l2h-208'></a></dl> | |
| 88 | ||
| 89 | <P> | |
| 90 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 91 | <td><nobr><b><tt id='l2h-209' xml:id='l2h-209' class="method">__setattr__</tt></b>(</nobr></td> | |
| 92 | <td><var>self, name, value</var>)</td></tr></table></dt> | |
| 93 | <dd> | |
| 94 | Called when an attribute assignment is attempted. This is called | |
| 95 | instead of the normal mechanism (i.e. store the value in the instance | |
| 96 | dictionary). <var>name</var> is the attribute name, <var>value</var> is the | |
| 97 | value to be assigned to it. | |
| 98 | ||
| 99 | <P> | |
| 100 | If <tt class="method">__setattr__()</tt> wants to assign to an instance attribute, it | |
| 101 | should not simply execute "<tt class="samp">self.<var>name</var> = value</tt>" -- this | |
| 102 | would cause a recursive call to itself. Instead, it should insert the | |
| 103 | value in the dictionary of instance attributes, e.g., | |
| 104 | "<tt class="samp">self.__dict__[<var>name</var>] = value</tt>". For new-style classes, | |
| 105 | rather than accessing the instance dictionary, it should call the base | |
| 106 | class method with the same name, for example, | |
| 107 | "<tt class="samp">object.__setattr__(self, name, value)</tt>". | |
| 108 | <a id='l2h-211' xml:id='l2h-211'></a></dl> | |
| 109 | ||
| 110 | <P> | |
| 111 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 112 | <td><nobr><b><tt id='l2h-212' xml:id='l2h-212' class="method">__delattr__</tt></b>(</nobr></td> | |
| 113 | <td><var>self, name</var>)</td></tr></table></dt> | |
| 114 | <dd> | |
| 115 | Like <tt class="method">__setattr__()</tt> but for attribute deletion instead of | |
| 116 | assignment. This should only be implemented if "<tt class="samp">del | |
| 117 | obj.<var>name</var></tt>" is meaningful for the object. | |
| 118 | </dl> | |
| 119 | ||
| 120 | <P> | |
| 121 | ||
| 122 | <p><br /></p><hr class='online-navigation' /> | |
| 123 | <div class='online-navigation'> | |
| 124 | <!--Table of Child-Links--> | |
| 125 | <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a> | |
| 126 | ||
| 127 | <UL CLASS="ChildLinks"> | |
| 128 | <LI><A href="new-style-attribute-access.html">3.3.2.1 More attribute access for new-style classes</a> | |
| 129 | <LI><A href="descriptors.html">3.3.2.2 Implementing Descriptors</a> | |
| 130 | <LI><A href="descriptor-invocation.html">3.3.2.3 Invoking Descriptors</a> | |
| 131 | <LI><A href="slots.html">3.3.2.4 __slots__</a> | |
| 132 | </ul> | |
| 133 | <!--End of Table of Child-Links--> | |
| 134 | </div> | |
| 135 | ||
| 136 | <DIV CLASS="navigation"> | |
| 137 | <div class='online-navigation'> | |
| 138 | <p></p><hr /> | |
| 139 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
| 140 | <tr> | |
| 141 | <td class='online-navigation'><a rel="prev" title="3.3.1 Basic customization" | |
| 142 | href="customization.html"><img src='../icons/previous.png' | |
| 143 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 144 | <td class='online-navigation'><a rel="parent" title="3.3 Special method names" | |
| 145 | href="specialnames.html"><img src='../icons/up.png' | |
| 146 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
| 147 | <td class='online-navigation'><a rel="next" title="3.3.2.1 More attribute access" | |
| 148 | href="new-style-attribute-access.html"><img src='../icons/next.png' | |
| 149 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
| 150 | <td align="center" width="100%">Python Reference Manual</td> | |
| 151 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
| 152 | href="contents.html"><img src='../icons/contents.png' | |
| 153 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
| 154 | <td class='online-navigation'><img src='../icons/blank.png' | |
| 155 | border='0' height='32' alt='' width='32' /></td> | |
| 156 | <td class='online-navigation'><a rel="index" title="Index" | |
| 157 | href="genindex.html"><img src='../icons/index.png' | |
| 158 | border='0' height='32' alt='Index' width='32' /></A></td> | |
| 159 | </tr></table> | |
| 160 | <div class='online-navigation'> | |
| 161 | <b class="navlabel">Previous:</b> | |
| 162 | <a class="sectref" rel="prev" href="customization.html">3.3.1 Basic customization</A> | |
| 163 | <b class="navlabel">Up:</b> | |
| 164 | <a class="sectref" rel="parent" href="specialnames.html">3.3 Special method names</A> | |
| 165 | <b class="navlabel">Next:</b> | |
| 166 | <a class="sectref" rel="next" href="new-style-attribute-access.html">3.3.2.1 More attribute access</A> | |
| 167 | </div> | |
| 168 | </div> | |
| 169 | <hr /> | |
| 170 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
| 171 | </DIV> | |
| 172 | <!--End of Navigation Panel--> | |
| 173 | <ADDRESS> | |
| 174 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. | |
| 175 | </ADDRESS> | |
| 176 | </BODY> | |
| 177 | </HTML> |