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<title>2.3.3 Comparisons </title>
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<H2><A NAME="SECTION004330000000000000000"></A><A NAME="comparisons"></A>
<BR>
2.3.3 Comparisons
</H2>

<P>
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> &lt;
<var>y</var> &lt;= <var>z</var></code> is equivalent to <code><var>x</var> &lt; <var>y</var> and
<var>y</var> &lt;= <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> &lt;
<var>y</var></code> is found to be false).
<a id='l2h-108' xml:id='l2h-108'></a>
<P>
This table summarizes the comparison operations:

<P>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="center">Operation</th>
      <th class="left"  >Meaning</th>
      <th class="center">Notes</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="center" valign="baseline"><code>&lt;</code></td>
        <td class="left"  >strictly less than</td>
        <td class="center"></td></tr>
    <tr><td class="center" valign="baseline"><code>&lt;=</code></td>
        <td class="left"  >less than or equal</td>
        <td class="center"></td></tr>
    <tr><td class="center" valign="baseline"><code>&gt;</code></td>
        <td class="left"  >strictly greater than</td>
        <td class="center"></td></tr>
    <tr><td class="center" valign="baseline"><code>&gt;=</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>&lt;&gt;</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>
</table></div>
<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>
<P>
Notes:

<P>
<DL>
<DT><STRONG>(1)</STRONG></DT>
<DD><code>&lt;&gt;</code> and <code>!=</code> are alternate spellings for the same operator.
<code>!=</code> is the preferred spelling; <code>&lt;&gt;</code> is obsolescent.

<P>
</DD>
</DL>

<P>
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>&lt;</code>, <code>&lt;=</code>, <code>&gt;</code> and <code>&gt;=</code>
operators will raise a <tt class="exception">TypeError</tt> exception when any operand
is a complex number.
<a id='l2h-113' xml:id='l2h-113'></a><a id='l2h-114' xml:id='l2h-114'></a>
<P>
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
<em class="citetitle"><a
 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.

<P>
<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.

<P>
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).

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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