diff options
| -rw-r--r-- | Doc/tutorial/datastructures.rst | 30 | ||||
| -rw-r--r-- | Misc/ACKS | 1 |
2 files changed, 22 insertions, 9 deletions
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst index 83b3012..54f442d 100644 --- a/Doc/tutorial/datastructures.rst +++ b/Doc/tutorial/datastructures.rst @@ -354,17 +354,31 @@ A tuple consists of a number of values separated by commas, for instance:: ... 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). - -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. +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. + +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 @@ -393,8 +407,6 @@ many variables on the left side of the equals sign as there are elements in the 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: @@ -1092,6 +1092,7 @@ Larry Wall Kevin Walzer Rodrigo Steinmuller Wanderley Greg Ward +Zachary Ware Barry Warsaw Steve Waterbury Bob Watson |