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<title>2.3.3 Comparisons
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<H2><A NAME=
"SECTION004330000000000000000"></A><A NAME=
"comparisons"></A>
Comparison operations are supported by all objects. They all have the
same priority (which is higher than that of the Boolean operations).
Comparisons can be chained arbitrarily; for example,
<code><var>x
</var> <
<var>y
</var> <=
<var>z
</var></code> is equivalent to
<code><var>x
</var> < <var>y
</var> and
<var>y
</var> <=
<var>z
</var></code>, except that
<var>y
</var> is evaluated only once (but
in both cases
<var>z
</var> is not evaluated at all when
<code><var>x
</var> <
<var>y
</var></code> is found to be false).
<a id='l2h-
108' xml:id='l2h-
108'
></a>
This table summarizes the comparison operations:
<div class=
"center"><table class=
"realtable">
<th class=
"center">Operation
</th>
<th class=
"left" >Meaning
</th>
<th class=
"center">Notes
</th>
<tr><td class=
"center" valign=
"baseline"><code><</code></td>
<td class=
"left" >strictly less than
</td>
<td class=
"center"></td></tr>
<tr><td class=
"center" valign=
"baseline"><code><=
</code></td>
<td class=
"left" >less than or equal
</td>
<td class=
"center"></td></tr>
<tr><td class=
"center" valign=
"baseline"><code>></code></td>
<td class=
"left" >strictly greater than
</td>
<td class=
"center"></td></tr>
<tr><td class=
"center" valign=
"baseline"><code>>=
</code></td>
<td class=
"left" >greater than or equal
</td>
<td class=
"center"></td></tr>
<tr><td class=
"center" valign=
"baseline"><code>==
</code></td>
<td class=
"left" >equal
</td>
<td class=
"center"></td></tr>
<tr><td class=
"center" valign=
"baseline"><code>!=
</code></td>
<td class=
"left" >not equal
</td>
<td class=
"center">(
1)
</td></tr>
<tr><td class=
"center" valign=
"baseline"><code><></code></td>
<td class=
"left" >not equal
</td>
<td class=
"center">(
1)
</td></tr>
<tr><td class=
"center" valign=
"baseline"><code>is
</code></td>
<td class=
"left" >object identity
</td>
<td class=
"center"></td></tr>
<tr><td class=
"center" valign=
"baseline"><code>is not
</code></td>
<td class=
"left" >negated object identity
</td>
<td class=
"center"></td></tr></tbody>
<a id='l2h-
109' xml:id='l2h-
109'
></a><a id='l2h-
110' xml:id='l2h-
110'
></a> <a id='l2h-
111' xml:id='l2h-
111'
></a><a id='l2h-
112' xml:id='l2h-
112'
></a>
<DT><STRONG>(
1)
</STRONG></DT>
<DD><code><></code> and
<code>!=
</code> are alternate spellings for the same operator.
<code>!=
</code> is the preferred spelling;
<code><></code> is obsolescent.
Objects of different types, except different numeric types and different string types, never
compare equal; such objects are ordered consistently but arbitrarily
(so that sorting a heterogeneous array yields a consistent result).
Furthermore, some types (for example, file objects) support only a
degenerate notion of comparison where any two objects of that type are
unequal. Again, such objects are ordered arbitrarily but
consistently. The
<code><</code>,
<code><=
</code>,
<code>></code> and
<code>>=
</code>
operators will raise a
<tt class=
"exception">TypeError
</tt> exception when any operand
<a id='l2h-
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113'
></a><a id='l2h-
114' xml:id='l2h-
114'
></a>
Instances of a class normally compare as non-equal unless the class
<a id='l2h-
116' xml:id='l2h-
116'
></a>defines the
<tt class=
"method">__cmp__()
</tt> method. Refer to the
href=
"../ref/customization.html"
title=
"Python Reference Manual"
>Python Reference Manual
</a></em> for
information on the use of this method to effect object comparisons.
<strong>Implementation note:
</strong> Objects of different types except
numbers are ordered by their type names; objects of the same types
that don't support proper comparison are ordered by their address.
Two more operations with the same syntactic priority,
"<tt class="samp
">in</tt>"<a id='l2h-
117' xml:id='l2h-
117'
></a> and
"<tt class="samp
">not in</tt>"<a id='l2h-
118' xml:id='l2h-
118'
></a>, are supported
only by sequence types (below).
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<span class=
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2.4.2, documentation updated on
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2005.
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