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<H2><A NAME="SECTION007240000000000000000"></A><A NAME="lists"></A>
<BR>
5.2.4 List displays
</H2>
<a id='l2h-344' xml:id='l2h-344'></a><a id='l2h-345' xml:id='l2h-345'></a>
<P>
A list display is a possibly empty series of expressions enclosed in
square brackets:
<P>
<dl><dd class="grammar">
<div class="productions">
<table>
<tr>
<td><a id='tok-test' xml:id='tok-test'>test</a></td>
<td>::=</td>
<td><a class='grammartoken' href="Booleans.html#tok-and_test">and_test</a> ( "or" <a class='grammartoken' href="Booleans.html#tok-and_test">and_test</a> )*
| <a class='grammartoken' href="lambdas.html#tok-lambda_form">lambda_form</a></td></tr>
<tr>
<td><a id='tok-testlist' xml:id='tok-testlist'>testlist</a></td>
<td>::=</td>
<td><a class='grammartoken' href="lists.html#tok-test">test</a> ( "," <a class='grammartoken' href="lists.html#tok-test">test</a> )* [ "," ]</td></tr>
<tr>
<td><a id='tok-list_display' xml:id='tok-list_display'>list_display</a></td>
<td>::=</td>
<td>"[" [<a class='grammartoken' href="lists.html#tok-listmaker">listmaker</a>] "]"</td></tr>
<tr>
<td><a id='tok-listmaker' xml:id='tok-listmaker'>listmaker</a></td>
<td>::=</td>
<td><a class='grammartoken' href="Booleans.html#tok-expression">expression</a> ( <a class='grammartoken' href="lists.html#tok-list_for">list_for</a>
| ( "," <a class='grammartoken' href="Booleans.html#tok-expression">expression</a> )* [","] )</td></tr>
<tr>
<td><a id='tok-list_iter' xml:id='tok-list_iter'>list_iter</a></td>
<td>::=</td>
<td><a class='grammartoken' href="lists.html#tok-list_for">list_for</a> | <a class='grammartoken' href="lists.html#tok-list_if">list_if</a></td></tr>
<tr>
<td><a id='tok-list_for' xml:id='tok-list_for'>list_for</a></td>
<td>::=</td>
<td>"for" <a class='grammartoken' href="exprlists.html#tok-expression_list">expression_list</a> "in" <a class='grammartoken' href="lists.html#tok-testlist">testlist</a>
[<a class='grammartoken' href="lists.html#tok-list_iter">list_iter</a>]</td></tr>
<tr>
<td><a id='tok-list_if' xml:id='tok-list_if'>list_if</a></td>
<td>::=</td>
<td>"if" <a class='grammartoken' href="lists.html#tok-test">test</a> [<a class='grammartoken' href="lists.html#tok-list_iter">list_iter</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 list display yields a new list object. Its contents are specified
by providing either a list of expressions or a list comprehension.
<a id='l2h-346' xml:id='l2h-346'></a>When a comma-separated list of expressions is supplied, its elements are
evaluated from left to right and placed into the list object in that
order. When a list comprehension is supplied, it consists of a
single expression followed by at least one <tt class="keyword">for</tt> clause and zero or
more <tt class="keyword">for</tt> or <tt class="keyword">if</tt> clauses. In this
case, the elements of the new list are those that would be produced
by considering each of the <tt class="keyword">for</tt> or <tt class="keyword">if</tt> clauses a block,
nesting from
left to right, and evaluating the expression to produce a list element
each time the innermost block is reached<A NAME="tex2html4"
HREF="#foot4519"><SUP>5.1</SUP></A>.
<a id='l2h-347' xml:id='l2h-347'></a><a id='l2h-348' xml:id='l2h-348'></a>
<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot4519">... reached</A><A
href="lists.html#tex2html4"><SUP>5.1</SUP></A></DT>
<DD>In Python 2.3, a
list comprehension "leaks" the control variables of each
"<tt class="samp">for</tt>" it contains into the containing scope. However, this
behavior is deprecated, and relying on it will not work once this
bug is fixed in a future release
</DD>
</DL>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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