Python内置函数(58)——slice
英文文档:
- class
slice
(stop) - class
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 toNone
. Slice objects have read-only data attributesstart
,stop
andstep
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]
ora[start:stop, i]
. Seeitertools.islice()
for an alternate version that returns an iterator.
说明:
1. 函数实际上是一个切片类的构造函数,返回一个切片对象。
2. 切片对象由3个属性start、stop、step组成,start和step默认值为None。切片对象主要用于对序列对象进行切片取对应元素。
>>> 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]
3. 对应切片对象的3个属性start、stop、step,slice函数也有3个对应的参数start、stop、step,其值分别会付给切片对象的start、stop、step。
>>> 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]