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<H2><A NAME="SECTION007230000000000000000"></A><A NAME="parenthesized"></A>
<a id='l2h-340' xml:id='l2h-340'></a>
<BR>
5.2.3 Parenthesized forms
</H2>

<P>
A parenthesized form is an optional expression list enclosed in
parentheses:

<P>
<dl><dd class="grammar">
<div class="productions">
<table>
<tr>
    <td><a id='tok-parenth_form' xml:id='tok-parenth_form'>parenth_form</a></td>
    <td>::=</td>
    <td>"(" [<a class='grammartoken' href="exprlists.html#tok-expression_list">expression_list</a>] ")"</td></tr>
</table>
</div>
<a class="grammar-footer"
  href="grammar.txt" type="text/plain"
  >Download entire grammar as text.</a>
</dd></dl>

<P>
A parenthesized expression list yields whatever that expression list
yields: if the list contains at least one comma, it yields a tuple;
otherwise, it yields the single expression that makes up the
expression list.

<P>
An empty pair of parentheses yields an empty tuple object.  Since
tuples are immutable, the rules for literals apply (i.e., two
occurrences of the empty tuple may or may not yield the same object).
<a id='l2h-341' xml:id='l2h-341'></a>
<P>
Note that tuples are not formed by the parentheses, but rather by use
of the comma operator.  The exception is the empty tuple, for which
parentheses <em>are</em> required -- allowing unparenthesized ``nothing''
in expressions would cause ambiguities and allow common typos to
pass uncaught.
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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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