Python內建函數(19)-slice

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官方文檔

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.函數實際上是切片類的一個建構函式，返回一個切片對象

         2.切片對象由3個參數組成，start、stop、step組成，start和step預設是None。切片對象主要是對序列對象進行切片取元素

>>> help(slice) |      Return repr(self). |   |  indices(...) |      S.indices(len) -> (start, stop, stride) |       |      Assuming a sequence of length len, calculate the start and stop |      indices, and the stride length of the extended slice described by |      S. Out of bounds indices are clipped in a manner consistent with the |      handling of normal slices. |   |  ---------------------------------------------------------------------- |  Data descriptors defined here: |   |  start |   |  step |   |  stop |   |  ---------------------------------------------------------------------- |  Data and other attributes defined here: |   |  __hash__ = None

li = [11,22,33,44,55,66,77]ret1 = li[None:5:None]  #start,stem為Noneret2 = li[:5:] #同上print(ret1,ret2)#輸出#[11, 22, 33, 44, 55]  [11, 22, 33, 44, 55]ret3 = li[2:5:None] #step為Noneret4 = li[2:5:]print(ret3,ret4)    #同上#輸出#[33, 44, 55]#[33, 44, 55]ret5 = li[1:6:3]print(ret5)#輸出#[22, 55]

　　3.對應切片的3個屬性start、stop、step,slice函數也有3個對應的參數start、stop、step,其值會直接賦給切片對象的start、stop、step

#定義c1c1 = slice(5)print(c1)#輸出#slice(None, 5, None)#定義c2c2 = slice(2,5)print(c2)#輸出#slice(2, 5, None)#定義c3c3 = slice(1,6,3)print(c3)#輸出#slice(1, 6, 3)a = list(range(1,10))ret1 = a[c1]   #同a[:5:]一樣print(ret1)#輸出#[1, 2, 3, 4, 5]ret2 = a[c2]  #同a[2:5:]一樣print(ret2)#輸出#[3, 4, 5]ret3 = a[c3]  #同a[1:6:3]一樣print(ret3)#輸出#[2, 5]

 

Python內建函數(19)-slice