On 6/22/2011 11:45 AM, Chetan Harjani wrote:
why tuples are immutable whereas list are mutable?
Because tuples do not have mutation methods, which lists do.
Tuple and lists both have .__getitem__ but tuples do not have
.__setitem__ or .__delitem__ (or .append, .extend, .sort, or .reverse).
why when we do x=y where y is a list and then change a element in x, y
changes too( but the same is not the case when we change the whole value
in x ), whereas, in tuples when we change x, y is not affected and also
we cant change each individual element in tuple. Someone please clarify.
For specific answers, you should give specific examples.
(1,2)[0] = 3 does not work because there is no tuple.__setitem__. But note:
>>> a = ([1,2], 3)
>>> b = a
>>> a[0][0] = 4
>>> b
([4, 2], 3)
Tuples containing mutables are not immutable all the way down.
They are also not hashable (if any element is not hashable) and cannot
be used as dict keys.
>>> hash(a)
Traceback (most recent call last):
File "<pyshell#5>", line 1, in <module>
hash(a)
TypeError: unhashable type: 'list'
--
Terry Jan Reedy
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