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authorThomas Wouters <thomas@python.org>2007-09-04 09:03:59 (GMT)
committerThomas Wouters <thomas@python.org>2007-09-04 09:03:59 (GMT)
commit53de1902e7a9788d2d4b917b1b14b2a76171f0f4 (patch)
treefba8718f30de59099f654febc175a84e1454ffb1 /Doc
parentaeaa546d7eb025fe68bc76dbbcaf5b6a97740140 (diff)
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Update ref docs on slicing.
Diffstat (limited to 'Doc')
-rw-r--r--Doc/reference/expressions.rst43
1 files changed, 13 insertions, 30 deletions
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index 0994ea8..a5bfd43 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -513,14 +513,10 @@ or list). Slicings may be used as expressions or as targets in assignment or
:keyword:`del` statements. The syntax for a slicing:
.. productionlist::
- slicing: `simple_slicing` | `extended_slicing`
- simple_slicing: `primary` "[" `short_slice` "]"
- extended_slicing: `primary` "[" `slice_list` "]"
+ slicing: `primary` "[" `slice_list` "]"
slice_list: `slice_item` ("," `slice_item`)* [","]
slice_item: `expression` | `proper_slice`
- proper_slice: `short_slice` | `long_slice`
- short_slice: [`lower_bound`] ":" [`upper_bound`]
- long_slice: `short_slice` ":" [`stride`]
+ proper_slice: [`lower_bound`] ":" [`upper_bound`] [ ":" [`stride`] ]
lower_bound: `expression`
upper_bound: `expression`
stride: `expression`
@@ -530,36 +526,23 @@ expression list also looks like a slice list, so any subscription can be
interpreted as a slicing. Rather than further complicating the syntax, this is
disambiguated by defining that in this case the interpretation as a subscription
takes priority over the interpretation as a slicing (this is the case if the
-slice list contains no proper slice). Similarly, when the slice list has
-exactly one short slice and no trailing comma, the interpretation as a simple
-slicing takes priority over that as an extended slicing.
-
-.. XXX is the next paragraph stil correct?
-
-The semantics for a simple slicing are as follows. The primary must evaluate to
-a sequence object. The lower and upper bound expressions, if present, must
-evaluate to plain integers; defaults are zero and the ``sys.maxint``,
-respectively. If either bound is negative, the sequence's length is added to
-it. The slicing now selects all items with index *k* such that ``i <= k < j``
-where *i* and *j* are the specified lower and upper bounds. This may be an
-empty sequence. It is not an error if *i* or *j* lie outside the range of valid
-indexes (such items don't exist so they aren't selected).
+slice list contains no proper slice).
.. index::
single: start (slice object attribute)
single: stop (slice object attribute)
single: step (slice object attribute)
-The semantics for an extended slicing are as follows. The primary must evaluate
-to a mapping object, and it is indexed with a key that is constructed from the
-slice list, as follows. If the slice list contains at least one comma, the key
-is a tuple containing the conversion of the slice items; otherwise, the
-conversion of the lone slice item is the key. The conversion of a slice item
-that is an expression is that expression. The conversion of a proper slice is a
-slice object (see section :ref:`types`) whose :attr:`start`, :attr:`stop` and
-:attr:`step` attributes are the values of the expressions given as lower bound,
-upper bound and stride, respectively, substituting ``None`` for missing
-expressions.
+The semantics for a slicing are as follows. The primary must evaluate to a
+mapping object, and it is indexed with a key that is constructed from the
+slice list, as follows. If the slice list contains at least one comma, the
+key is a tuple containing the conversion of the slice items; otherwise, the
+conversion of the lone slice item is the key. The conversion of a slice
+item that is an expression is that expression. The conversion of a proper
+slice is a slice object (see section :ref:`types`) whose :attr:`start`,
+:attr:`stop` and :attr:`step` attributes are the values of the expressions
+given as lower bound, upper bound and stride, respectively, substituting
+``None`` for missing expressions.
.. _calls: