mac上输入python报错?报错

我写了一个python的文件叫abc.py，里面就是print 'hello world' ,然后在该目录下输入python进入python的命令行,进行了如下的操作
>>> import abc

>>> print(abc)

<module 'abc' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/abc.pyc'>
按理来说应该是打印出hello world的，于是我去上面显示的这个地址/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/abc.pyc
删除了三个文件:abc.py,abc.pyc,abc.pyo
但是当我再次输入python的时候就出现了下面的错误：
Traceback (most recent call last):

  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site.py", line 62, in <module>

    import os

  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.py", line 398, in <module>

    import UserDict

  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/UserDict.py", line 83, in <module>

    import _abcoll

  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/_abcoll.py", line 11, in <module>

    from abc import ABCMeta, abstractmethod

ImportError: No module named abc
我看了下_abcoll.py的第11行
from abc import ABCMeta, abstractmethod
请问为什么会出现这种情况，我应该如何解决？
谢谢