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分享求助帖，关于Python的切片
>>>numbers=[1,2,3,4,5,6,7,8,9,10]
>>>numbers[8:3:-1]
[9, 8, 7, 6, 5]
>>> numbers[:5:-2]
[10, 8]
这两条语句不太懂，谁能给解释下
>>>numbers[8:3:-1]
[9, 8, 7, 6, 5]
>>> numbers[:5:-2]
[10, 8]
这两条语句不太懂，谁能给解释下
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核动力蜗牛Killua 2012-03-19
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LS已经很清楚了
第一个是从numbers[8] -> numbers[3](不包括numbers[3]), 步长为-1，也就是倒着走
第二个是从number[0]开始，步长为-2，倒着走到numbers[5](不包括numbers[5])
第一个是从numbers[8] -> numbers[3](不包括numbers[3]), 步长为-1，也就是倒着走
第二个是从number[0]开始，步长为-2，倒着走到numbers[5](不包括numbers[5])
RabbitLBJ 2012-03-19
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1.先看第三个参数，如果该数为正，则从前往后数，如果为负，则从后往前数，如果非1，则是跳步来数
2.PYTHON总是左开右闭的，也就是说第一个参数要包括，第二个参数不包括
3.如果第一个参数没填，则自动设为第一个参数（根据第三个参数的正负判断是整数第一个还是倒数第一个）
4.如果第二个参数没填，则自动设定为最后一个参数（根据第三个参数的正负判断是整数第一个还是倒数第一个，另外这个参数不会包括进去【左开右闭】）
2.PYTHON总是左开右闭的，也就是说第一个参数要包括，第二个参数不包括
3.如果第一个参数没填，则自动设为第一个参数（根据第三个参数的正负判断是整数第一个还是倒数第一个）
4.如果第二个参数没填，则自动设定为最后一个参数（根据第三个参数的正负判断是整数第一个还是倒数第一个，另外这个参数不会包括进去【左开右闭】）
angel_su 2012-03-19
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练练英文自己翻翻手册，The Python Standard Library -> 5.6. Sequence Types 有几个注释：
...
s[i] i‘th item of s, origin 0 (3)
s[i:j] slice of s from i to j (3)(4)
s[i:j:k] slice of s from i to j with step k (3)(5)
...
If i or j is negative, the index is relative to the end of the string: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.
The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty.
The slice of s from i to j with step k is defined as the sequence of items with index x = i + n*k such that 0 <= n < (j-i)/k. In other words, the indices are i, i+k, i+2*k, i+3*k and so on, stopping when j is reached (but never including j). If i or j is greater than len(s), use len(s). If i or j are omitted or None, they become “end” values (which end depends on the sign of k). Note, k cannot be zero. If k is None, it is treated like 1.
...
...
s[i] i‘th item of s, origin 0 (3)
s[i:j] slice of s from i to j (3)(4)
s[i:j:k] slice of s from i to j with step k (3)(5)
...
If i or j is negative, the index is relative to the end of the string: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.
The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty.
The slice of s from i to j with step k is defined as the sequence of items with index x = i + n*k such that 0 <= n < (j-i)/k. In other words, the indices are i, i+k, i+2*k, i+3*k and so on, stopping when j is reached (but never including j). If i or j is greater than len(s), use len(s). If i or j are omitted or None, they become “end” values (which end depends on the sign of k). Note, k cannot be zero. If k is None, it is treated like 1.
...
Gloveing 2012-03-18
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slice([start], stop[, step])
Return a slice object representing the set of indices specified by range(start, stop, step). The start and step arguments default to None. Slice objects have read-only data attributes start, stop and step which merely return the argument values (or their default). They have no other explicit functionality; however they are used by Numerical Python and other third party extensions. Slice objects are also generated when extended indexing syntax is used. For example: a[start:stop:step] or a[start:stop, i]. See itertools.islice() for an alternate version that returns an iterator.
Return a slice object representing the set of indices specified by range(start, stop, step). The start and step arguments default to None. Slice objects have read-only data attributes start, stop and step which merely return the argument values (or their default). They have no other explicit functionality; however they are used by Numerical Python and other third party extensions. Slice objects are also generated when extended indexing syntax is used. For example: a[start:stop:step] or a[start:stop, i]. See itertools.islice() for an alternate version that returns an iterator.
