应用场景：

根据线程数，分割任务列表；

####功能：将list对象N等分
def div_list(ls,n):
	if not isinstance(ls,list) or not isinstance(n,int):
		return []
	ls_len = len(ls)
	if n<=0 or 0==ls_len:
		return []
	if n > ls_len:
		return []
	elif n == ls_len:
		return [[i] for i in ls]
	else:
		j = ls_len/n
		k = ls_len%n
		### j,j,j,...(前面有n-1个j),j+k
		#步长j,次数n-1
		ls_return = []
		for i in xrange(0,(n-1)*j,j):
			ls_return.append(ls[i:i+j])
		#算上末尾的j+k
		ls_return.append(ls[(n-1)*j:])
		return ls_return

if 0:
	print div_list(3,3)
	print div_list([3],'3')
	print div_list([3],-1)
	print div_list([],2)
	print div_list([3],2)
	print div_list([3,4,5,6],4)
	print div_list([3,4,5,6,7,8,9,10,11,12,13,14,15],3)