s7v7nislands 写道:
Thanks for your reply! Sorry for my poor english!
On Sep 10, 12:33 pm, Chris Rebert <c...@rebertia.com> wrote:
On Wed, Sep 9, 2009 at 9:00 PM, s7v7nislands<s7v7nisla...@gmail.com> wrote:
hi all:
what is the s.index() mean? does the index() change the s?
It tells you the index of the first instance of the given element in
the sequence. Or, to quote the docs:
s.index(x[, i[, j]]) --- return smallest k such that s[k] == x and
i <= k < j
No, .index() does not modify the sequence itself.
I known index() does not modify the sequence itself. my question is so
why the doc put the index() method in the mutable sequence types list?
It applies to both mutable and immutable sequence.
In python2.6 doc (6.6.4. Mutable Sequence Types), Note 4:
Raises ValueError when x is not found in s. When a negative index is
passed as the second or third parameter to the index() method, the
list length is added, as for slice indices. If it is still negative,
it is truncated to zero, as for slice indices.
Changed in version 2.3: Previously, index() didn’t have arguments for
specifying start and stop positions.
Nothing in the above says anything about modifying a sequence...
When a negative index is passed as the second or third parameter to
the index() method, the list length is added, as for slice indices.
I don't understand the mean. the list length is added, why? if it
changed, the original will change ?
It is just the common rule for negative index.
eg. s[-k] == s[-k + len(s)].
The original sequence is not changed.
who can give a example? and why the s.remove() also point to note 4?
Because it has the same behavior when the item is not present in the sequence.
Examples using lists:
assert ["c", "a", "b", "c", "c"].index("c", 1) == 3
try:
["a", "b"].index("c")
except ValueError:
print "'c' was not in the list"
else:
raise RuntimeError, "Should never get here"
x = ["a", "b", "c"]
x.remove("b")
assert len(x) == 2 and x[0] == "a" and x[1] == "c"
I want a example, maybe: use the a negative index is passed as the
second or third parameter, and see the length changed.
x = 'abcde'
x.index('d', -3, -1) = x.index('d', 2, 4) = 3
x.index('a', -3, -1) = x.index('a', 2, 4) = -1, raise ValueError
Is the document wrong?
No. What made you think so?
Sorry for my poor english. do you understand me now? thanks!
Cheers,
Chris
--http://blog.rebertia.com
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