python实现输出一个序列的所有子序列示例

def sub(arr):
 finish=[]
 size = len(arr)
 end = 1 << size #end=2**size
 for index in range(end): # shift index
  array = []
  for j in range(size):
   # 00,01,10,11 is symmetrical
   if (index >> j) % 2: # this result is 1, so do not have to write ==
    array.append(arr[j])
  # print(array)
  finish.append(array)
 return finish