Python內建函數(58)——slice，python內建58slice

Python內建函數(58)——slice，python內建58slice

英文文檔：

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 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.

 

說明：

　　1. 函數實際上是一個切片類的建構函式，返回一個切片對象。

　　2. 切片對象由3個屬性start、stop、step組成，start和step預設值為None。切片對象主要用於對序列對象進行切片取對應元素。

>>> 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顯式為None[0, 1, 2, 3, 4]>>> a[:5:] # start step預設為None[0, 1, 2, 3, 4]>>> a[2:5:None] # step顯式為None[2, 3, 4]>>> a[2:5:] # step預設為None[2, 3, 4]>>> a[1:10:3][1, 4, 7]

　　3. 對應切片對象的3個屬性start、stop、step，slice函數也有3個對應的參數start、stop、step，其值分別會付給切片對象的start、stop、step。

>>> c1 = slice(5) # 定義c1>>> c1slice(None, 5, None)>>> c2 = slice(2,5) # 定義c2>>> c2slice(2, 5, None)>>> c3 = slice(1,10,3) # 定義c3>>> c3slice(1, 10, 3)>>> a[c1] # 和a[:5:]結果相同[0, 1, 2, 3, 4]>>> a[c2] # 和a[2:5:]結果相同[2, 3, 4]>>> a[c3] # 和a[1:10:3]結果相同[1, 4, 7]