f.seek(0,os.SEEK_SET) 出错了

In [9]: f.seek(0,os.SEEK_SET)
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-9-0f708da6b469> in <module>()
----> 1 f.seek(0,os.SEEK_SET)

NameError: name 'os' is not defined