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bpo-46725: Document starred expressions in for statements (GH-31481)
Automerge-Triggered-By: GH:pablogsal
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@ -154,17 +154,20 @@ The :keyword:`for` statement is used to iterate over the elements of a sequence
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(such as a string, tuple or list) or other iterable object:
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(such as a string, tuple or list) or other iterable object:
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.. productionlist:: python-grammar
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.. productionlist:: python-grammar
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for_stmt: "for" `target_list` "in" `expression_list` ":" `suite`
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for_stmt: "for" `target_list` "in" `starred_list` ":" `suite`
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: ["else" ":" `suite`]
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: ["else" ":" `suite`]
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The expression list is evaluated once; it should yield an iterable object. An
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The expression list is evaluated once; it should yield an iterable object. An
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iterator is created for the result of the ``expression_list``. The suite is
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iterator is created for the result of the ``starred_list``. The expression
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then executed once for each item provided by the iterator, in the order returned
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list can contain starred elements (``*x, *y``) that will be unpacked in the
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by the iterator. Each item in turn is assigned to the target list using the
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final iterator (as when constructing a ``tuple`` or ``list`` literal). The
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standard rules for assignments (see :ref:`assignment`), and then the suite is
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suite is then executed once for each item provided by the iterator, in the
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executed. When the items are exhausted (which is immediately when the sequence
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order returned by the iterator. Each item in turn is assigned to the target
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is empty or an iterator raises a :exc:`StopIteration` exception), the suite in
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list using the standard rules for assignments (see :ref:`assignment`), and then
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the :keyword:`!else` clause, if present, is executed, and the loop terminates.
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the suite is executed. When the items are exhausted (which is immediately when
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the sequence is empty or an iterator raises a :exc:`StopIteration` exception),
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the suite in the :keyword:`!else` clause, if present, is executed, and the loop
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terminates.
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.. index::
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.. index::
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statement: break
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statement: break
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@ -196,6 +199,8 @@ the built-in function :func:`range` returns an iterator of integers suitable to
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emulate the effect of Pascal's ``for i := a to b do``; e.g., ``list(range(3))``
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emulate the effect of Pascal's ``for i := a to b do``; e.g., ``list(range(3))``
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returns the list ``[0, 1, 2]``.
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returns the list ``[0, 1, 2]``.
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.. versionchanged:: 3.11
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Starred elements are now allowed in the expression list.
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.. _try:
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.. _try:
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.. _except:
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.. _except:
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@ -160,6 +160,9 @@ traceback. (Contributed by Irit Katriel in :issue:`45607`.)
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Other Language Changes
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Other Language Changes
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======================
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======================
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* Starred expressions can be used in :ref:`for statements<for>`. (See
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:issue:`46725` for more details.)
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* Asynchronous comprehensions are now allowed inside comprehensions in
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* Asynchronous comprehensions are now allowed inside comprehensions in
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asynchronous functions. Outer comprehensions implicitly become
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asynchronous functions. Outer comprehensions implicitly become
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asynchronous. (Contributed by Serhiy Storchaka in :issue:`33346`.)
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asynchronous. (Contributed by Serhiy Storchaka in :issue:`33346`.)
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@ -1403,6 +1403,12 @@ def __getitem__(self, i):
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result.append(x)
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result.append(x)
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self.assertEqual(result, [1, 2, 3])
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self.assertEqual(result, [1, 2, 3])
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result = []
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a = b = c = [1, 2, 3]
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for x in *a, *b, *c:
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result.append(x)
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self.assertEqual(result, 3 * a)
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def test_try(self):
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def test_try(self):
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### try_stmt: 'try' ':' suite (except_clause ':' suite)+ ['else' ':' suite]
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### try_stmt: 'try' ':' suite (except_clause ':' suite)+ ['else' ':' suite]
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### | 'try' ':' suite 'finally' ':' suite
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### | 'try' ':' suite 'finally' ':' suite
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