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54 | 2.2.4 Object Comparison</A> | |
55 | </H2> | |
56 | ||
57 | <P> | |
58 | <div class="verbatim"><pre> | |
59 | cmpfunc tp_compare; | |
60 | </pre></div> | |
61 | ||
62 | <P> | |
63 | The <tt class="member">tp_compare</tt> handler is called when comparisons are needed | |
64 | and the object does not implement the specific rich comparison method | |
65 | which matches the requested comparison. (It is always used if defined | |
66 | and the <tt class="cfunction">PyObject_Compare()</tt> or <tt class="cfunction">PyObject_Cmp()</tt> | |
67 | functions are used, or if <tt class="function">cmp()</tt> is used from Python.) | |
68 | It is analogous to the <tt class="method">__cmp__()</tt> method. This function | |
69 | should return <code>-1</code> if <var>obj1</var> is less than | |
70 | <var>obj2</var>, <code>0</code> if they are equal, and <code>1</code> if | |
71 | <var>obj1</var> is greater than | |
72 | <var>obj2</var>. | |
73 | (It was previously allowed to return arbitrary negative or positive | |
74 | integers for less than and greater than, respectively; as of Python | |
75 | 2.2, this is no longer allowed. In the future, other return values | |
76 | may be assigned a different meaning.) | |
77 | ||
78 | <P> | |
79 | A <tt class="member">tp_compare</tt> handler may raise an exception. In this case it | |
80 | should return a negative value. The caller has to test for the | |
81 | exception using <tt class="cfunction">PyErr_Occurred()</tt>. | |
82 | ||
83 | <P> | |
84 | Here is a sample implementation: | |
85 | ||
86 | <P> | |
87 | <div class="verbatim"><pre> | |
88 | static int | |
89 | newdatatype_compare(newdatatypeobject * obj1, newdatatypeobject * obj2) | |
90 | { | |
91 | long result; | |
92 | ||
93 | if (obj1->obj_UnderlyingDatatypePtr->size < | |
94 | obj2->obj_UnderlyingDatatypePtr->size) { | |
95 | result = -1; | |
96 | } | |
97 | else if (obj1->obj_UnderlyingDatatypePtr->size > | |
98 | obj2->obj_UnderlyingDatatypePtr->size) { | |
99 | result = 1; | |
100 | } | |
101 | else { | |
102 | result = 0; | |
103 | } | |
104 | return result; | |
105 | } | |
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