python内置函数之slice案例详解

>>> help(slice)
class slice(object)
 |  slice(stop)
 |  slice(start, stop[, step])
 |  
 |  Create a slice object.  This is used for extended slicing (e.g. a[0:10:2]).
 |  
 |  Methods defined here:
 |  
 |  ...#省略#
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  start
 |  
 |  step
 |  
 |  stop
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __hash__ = None

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> a[None:5:None] # start step显式为None
[0, 1, 2, 3, 4]
>>> a[:5:] # start step默认为None
[0, 1, 2, 3, 4]
>>> a[2:5:None] # step显式为None
[2, 3, 4]
>>> a[2:5:] # step默认为None
[2, 3, 4]
>>> a[1:10:3]
[1, 4, 7]

>>> c1 = slice(5) # 定义c1
>>> c1
slice(None, 5, None)
>>> c2 = slice(2,5) # 定义c2
>>> c2
slice(2, 5, None)
>>> c3 = slice(1,10,3) # 定义c3
>>> c3
slice(1, 10, 3)
>>> a[c1] # 和a[:5:]结果相同
[0, 1, 2, 3, 4]
>>> a[c2] # 和a[2:5:]结果相同
[2, 3, 4]
>>> a[c3] # 和a[1:10:3]结果相同
[1, 4, 7]