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<td><font face="Times New Roman, Times, Serif" size="4"><b>Appendix D<br>
Special Class Methods in Python</b></font></td>
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<td><font face="Times New Roman, Times, Serif" size="3">Special class
methods are an important feature of Python, making it an extremely
flexible language. All user-defined classes may provide implementations
of these methods, which are called or invoked whenever the appropriate
action is called for by the Python interpreter. You'll find detailed
discussion of all these methods in Chapter 13, ''Special Class Methods
in Python." What is listed here is intended only to jog your memory, not
to provide a detailed explanation. Therefore, the methods are listed
here in alphabetical order. A listing by use can be found at the
official Python Reference Manual: </font>
<font face="Times New Roman, Times, Serif" color="#0000ff" size="3">
<a href="http://www.python.org/doc/current/ref/index.html," target="_BLANK">
<u>http://www.python.org/doc/current/ref/index.html,</u></a></font><font face="Times New Roman, Times, Serif" size="3">
Section 3.3. Each explanation is preceded by the general use of the
method.</font></td>
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<td><font face="Times New Roman, Times, Serif" size="3">Note that in the
following methods, when it says "return the result" or something like
that, you need to create a new object to return. For instance, </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
x = x + y</font><font face="Times New Roman, Times, Serif" size="3">
uses <i>x</i> and <i>y</i> as inputs but creates a whole new object to
return, which is assigned to <i>x</i> after the calculation is
performed.</font><font face="Times New Roman, Times, Serif" color="#ffff00" size="3"><!-- break --></font></td>
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<td><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
<b>__abs__(<i>self)<br>
</i></b></font><font face="Times New Roman, Times, Serif" size="3">
Numeric; return the absolute value of </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> (no
sign).</font></td>
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<td><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
<b>__add__(<i>self,other)<br>
</i></b></font><font face="Times New Roman, Times, Serif" size="3">
Numeric and sequence; add </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> to
</font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><font face="Times New Roman, Times, Serif" size="3"> or
concatenate </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> and
</font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><i><font face="Times New Roman, Times, Serif" size="3">,</font></i><font face="Times New Roman, Times, Serif" size="3">
and return the result.</font></td>
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<td><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
<b>__and__(<i>self,other)<br>
</i></b></font><font face="Times New Roman, Times, Serif" size="3">
Numeric; return the result of bitwise </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
and'ing (&) <i>self</i></font><font face="Times New Roman, Times, Serif" size="3">
with </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><i><font face="Times New Roman, Times, Serif" size="3">.</font></i></td>
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<td><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
<b>__call__(<i>self[,args])<br>
</i></b></font><font face="Times New Roman, Times, Serif" size="3">
Class; if it makes sense to treat your class as a function, implement
this method; </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
args</i></font><font face="Times New Roman, Times, Serif" size="3"> are
optional.</font></td>
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<td><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
<b>__cmp__(<i>self,other)<br>
</i></b></font><font face="Times New Roman, Times, Serif" size="3">
Class, others; called by all comparison operations. Return </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3">-1</font><font face="Times New Roman, Times, Serif" size="3">
if </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> is <
</font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><i><font face="Times New Roman, Times, Serif" size="3">,</font></i><font face="Times New Roman, Times, Serif" size="3">
</font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3">0</font><font face="Times New Roman, Times, Serif" size="3">
if </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> and
</font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><font face="Times New Roman, Times, Serif" size="3"> are
equal, and </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3">1</font><font face="Times New Roman, Times, Serif" size="3">
if </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> is >
than </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><i><font face="Times New Roman, Times, Serif" size="3">.</font></i></td>
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<td><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">
<b>__coerce__(<i>self,other)<br>
</i></b></font><font face="Times New Roman, Times, Serif" size="3">
Numeric; called whenever </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
self</i></font><font face="Times New Roman, Times, Serif" size="3"> and
</font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><font face="Times New Roman, Times, Serif" size="3">
must be converted to a common type for some sort of arithmetic
operation. Usually, you convert </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><font face="Times New Roman, Times, Serif" size="3"> to
an instance of your class, although you could convert your class to
whatever type </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>
other</i></font><font face="Times New Roman, Times, Serif" size="3"> is.
Return a tuple: </font>
<font face="Courier New, Courier, Mono New, Courier, Mono" size="3"><i>(self,other)</i></font><i><font face="Times New Roman, Times, Serif" size="3">.</font></i></td>
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