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55 | <H2><A NAME="SECTION007230000000000000000"></A><A NAME="parenthesized"></A> | |
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58 | 5.2.3 Parenthesized forms | |
59 | </H2> | |
60 | ||
61 | <P> | |
62 | A parenthesized form is an optional expression list enclosed in | |
63 | parentheses: | |
64 | ||
65 | <P> | |
66 | <dl><dd class="grammar"> | |
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70 | <td><a id='tok-parenth_form' xml:id='tok-parenth_form'>parenth_form</a></td> | |
71 | <td>::=</td> | |
72 | <td>"(" [<a class='grammartoken' href="exprlists.html#tok-expression_list">expression_list</a>] ")"</td></tr> | |
73 | </table> | |
74 | </div> | |
75 | <a class="grammar-footer" | |
76 | href="grammar.txt" type="text/plain" | |
77 | >Download entire grammar as text.</a> | |
78 | </dd></dl> | |
79 | ||
80 | <P> | |
81 | A parenthesized expression list yields whatever that expression list | |
82 | yields: if the list contains at least one comma, it yields a tuple; | |
83 | otherwise, it yields the single expression that makes up the | |
84 | expression list. | |
85 | ||
86 | <P> | |
87 | An empty pair of parentheses yields an empty tuple object. Since | |
88 | tuples are immutable, the rules for literals apply (i.e., two | |
89 | occurrences of the empty tuple may or may not yield the same object). | |
90 | <a id='l2h-341' xml:id='l2h-341'></a> | |
91 | <P> | |
92 | Note that tuples are not formed by the parentheses, but rather by use | |
93 | of the comma operator. The exception is the empty tuple, for which | |
94 | parentheses <em>are</em> required -- allowing unparenthesized ``nothing'' | |
95 | in expressions would cause ambiguities and allow common typos to | |
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