Python中具有奇怪行为的字符串切割

我正试图通过Python程序获得树莓派的cpu利用率。

下面的bash语句非常有效:

top -n1 | grep %Cpu    
%Cpu(s): 35.6 us, 15.6 sy,  0.0 ni, 47.3 id,  0.1 wa,  0.0 hi,  1.4 si,  0.0 st

然而,当我试图在我的Python程序中剪切我需要的信息时,发生了一些奇怪的事情。左边的分隔符效果很好,但是右边的分隔符会使我的结果消失(只返回空格)

def get_cpu_utilization():
    statement = "top -n1 | grep %Cpu"
    result = check_output(statement, shell=True)
    # result = result[8:]  this works!
    # result = result[:14] doesn't work!
    #The statement below doesn't work either 
    result = result[8:14]
    print(result)

再一次,我得到的都是空白。。。

我在这里做错了什么?

编辑1:

在我的Mac上运行代码很好:

Python 2.7.10 (v2.7.10:15c95b7d81dc, May 23 2015, 09:33:12) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> result = "%Cpu(s): 39.3 us, 15.8 sy,  0.0 ni, 43.4 id,  0.1 wa,  0.0 hi,  1.3 si,  0.0 st"
>>> print(result[8:14])
 39.3 
>>> 

编辑2:

一步步让您了解发生了什么:

from subprocess import check_output


def get_cpu_utilization():
    statement = "top -n1 | grep %Cpu"
    result = check_output(statement, shell=True)
    print(result)
    result = result[8:]
    print(result)
    result = result[:6]
    print(result)
    result = result.strip()
    print repr(result)
    return result

这就是我得到的:

me@rpi $ sudo python cpu.py
%Cpu(s): 30.8 us, 15.2 sy,  0.0 ni, 52.6 id,  0.1 wa,  0.0 hi,  1.3 si,  0.0 st

 30.8 us, 15.2 sy,  0.0 ni, 52.6 id,  0.1 wa,  0.0 hi,  1.3 si,  0.0 st



me@rpi $