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实例+解释如下（表格）：关键是要明白python中数组的下标体系。一套从左往右，一套从右往左。
| A=np.array([1,2,3,4,5,6,7,8,9,0]) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 |
| 下标系一Index(Left to Right) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| 下标系二Index(Right to Left) | -10 | -9 | -8 | -7 | -6 | -5 | -4 | -3 | -2 | -1 |
| A[a:b:c] | a和b 确定：切片操作的范围(from a to b, exclude b.)， C 确定具体切片的pace和方向（例如：1表示Left to Right，pace=1. -1表示Right to Left，pace=1.）。 | |||||||||
| 实例：A[:3:1] | output: 1,2,3. 注：Index 3处对应的数组值4。1表示从左往右，步的大小是1。所以输出1，2，3 | |||||||||
| 实例：A[:-3:-1] | output:0,9 注：Index -3处对应的数组值8。-1表示从右往左，步的大小是1。所以输出0，9 | |||||||||
| 实例：A[:3:-1] | output:0,9,8,7,6,5 注：Index 3处对应的数组值4。-1表示从右往左，步的大小是1。所以输出0，9，8，7，6，5 | |||||||||
| 实例：A[:-3:1] |
output:0,9 注：Index -3处对应的数组值8。1表示从左往右，步的大小是1。所以输出1，2，3，4，5，6，7，8 |
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| 实例：A[-3::-1] |
output:8,7,6,5,4,3,2,1 注：Index -3处对应的数组值8。-1表示从右往左，步的大小是1。所以输出8,7,6,5,4,3,2,1 |
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1 import numpy as np 2 import sys 3 4 def main(): 5 A=np.array([1,2,3,4,5,6,7,8,9,0]) 6 B=A.copy() 7 print A 8 print ‘same as print A,‘,A[:] 9 print ‘same as print A,‘,A[::1] 10 print ‘reverse A,‘,A[::-1] 11 print ‘print all elements with 2 interval,‘,A[::2] 12 print ‘print elements from the 4th element with 2 interval,‘,A[3::2] 13 print ‘print elements from the last 4th element with 2 interval,‘,A[-3::2] 14 print ‘print elements from the 2nd to 5th element with 2 interval,‘,A[1:4:2] 15 print ‘reverse print all elements with 2 interval,‘,A[::-2] 16 print ‘reverse print elements from the 4th element with 2 interval,‘,A[3::-2] 17 print ‘reverse print elements from the last 4th element with 2 interval,‘,A[-3::-2] 18 #print A[a:b:c]: a and b determine range of slide. c determine the interval and direction (forth or reverse) 19 print A[:-3:-1] 20 print A[:3:1] 21 print A[:3:-1] 22 C=A[::-1] 23 C[0]=10 24 print ‘A is also changed as how does c change,‘,A 25 B[9]=0 26 print ‘A will not be affected when B change,‘,A 27 print ‘array slide from second element to the last one,‘,A[1:] 28 print ‘array slide from last second element to the first one,‘,A[:-1] 29 30 31 32 if __name__ == "__main__": 33 main()
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原文地址：http://www.cnblogs.com/1zhk/p/4929874.html
