求一个集合的所有真子集 Python

给定一个集合，元素均为正整数且不重复，求该集合的所有子集

 # -*- coding: utf-8 -*-
 """
 Created on Tue Oct 10 09:04:53 2017

 @author: nvidia
 """

 #!/usr/bin/python
 #coding=utf-8
 #求一个集合的所有真子集
 def getRealSubSet(fromList,toList):
   if(len(fromList) <= 1):
   return
   for id in range(len(fromList)):
   arr = [i for i in fromList if i != fromList[id]]
   getRealSubSet(arr,toList)
   #print arr
   if(toList.count(arr) == 0):
   toList.append(arr)

 li = []
 getRealSubSet([3,4,5],li)
 li.sort()
 print li

 #以上为第二题答案
 #after charging ,it was all right!

 """
 the down words are the result!
 Python 2.7.12 (default, Nov 19 2016, 06:48:10)
 Type "copyright", "credits" or "license" for more information.

 IPython 2.4.1 -- An enhanced Interactive Python.
 ? -> Introduction and overview of IPython's features.
 %quickref -> Quick reference.
 help -> Python's own help system.
 object? -> Details about 'object', use 'object??' for extra details.
 %guiref -> A brief reference about the graphical user interface.

 In [1]: runfile('/home/nvidia/Documents/work/20171010.py', wdir='/home/nvidia/Documents/work')
 [[3], [3, 4], [3, 5], [4], [4, 5], [5]]

 In [2]: 

 """