[Python-checkins] cpython (2.7): #14840: Add a bit on the difference between tuples and lists. Initial patch by
ezio.melotti
python-checkins at python.org
Sun Jun 17 14:13:54 CEST 2012
http://hg.python.org/cpython/rev/bb63919cde6e
changeset: 77495:bb63919cde6e
branch: 2.7
parent: 77488:ac2f5067c220
user: Ezio Melotti <ezio.melotti at gmail.com>
date: Sun Jun 17 14:10:59 2012 +0200
summary:
#14840: Add a bit on the difference between tuples and lists. Initial patch by Zachary Ware.
files:
Doc/tutorial/datastructures.rst | 28 +++++++++++++++------
Misc/ACKS | 1 +
2 files changed, 21 insertions(+), 8 deletions(-)
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst
--- a/Doc/tutorial/datastructures.rst
+++ b/Doc/tutorial/datastructures.rst
@@ -423,17 +423,31 @@
... u = t, (1, 2, 3, 4, 5)
>>> u
((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
+ >>> # Tuples are immutable:
+ ... t[0] = 88888
+ Traceback (most recent call last):
+ File "<stdin>", line 1, in <module>
+ TypeError: 'tuple' object does not support item assignment
+ >>> # but they can contain mutable objects:
+ ... v = ([1, 2, 3], [3, 2, 1])
+ >>> v
+ ([1, 2, 3], [3, 2, 1])
+
As you see, on output tuples are always enclosed in parentheses, so that nested
tuples are interpreted correctly; they may be input with or without surrounding
parentheses, although often parentheses are necessary anyway (if the tuple is
-part of a larger expression).
+part of a larger expression). It is not possible to assign to the individual
+items of a tuple, however it is possible to create tuples which contain mutable
+objects, such as lists.
-Tuples have many uses. For example: (x, y) coordinate pairs, employee records
-from a database, etc. Tuples, like strings, are immutable: it is not possible
-to assign to the individual items of a tuple (you can simulate much of the same
-effect with slicing and concatenation, though). It is also possible to create
-tuples which contain mutable objects, such as lists.
+Though tuples may seem similar to lists, they are often used in different
+situations and for different purposes.
+Tuples are :term:`immutable`, and usually contain an heterogeneous sequence of
+elements that are accessed via unpacking (see later in this section) or indexing
+(or even by attribute in the case of :func:`namedtuples <collections.namedtuple>`).
+Lists are :term:`mutable`, and their elements are usually homogeneous and are
+accessed by iterating over the list.
A special problem is the construction of tuples containing 0 or 1 items: the
syntax has some extra quirks to accommodate these. Empty tuples are constructed
@@ -462,8 +476,6 @@
sequence. Note that multiple assignment is really just a combination of tuple
packing and sequence unpacking.
-.. XXX Add a bit on the difference between tuples and lists.
-
.. _tut-sets:
diff --git a/Misc/ACKS b/Misc/ACKS
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -900,6 +900,7 @@
Larry Wall
Kevin Walzer
Greg Ward
+Zachary Ware
Barry Warsaw
Steve Waterbury
Bob Watson
--
Repository URL: http://hg.python.org/cpython
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