def seek(self, offset, whence=SEEK_SET):
    if whence == BlobReader.SEEK_CUR:
      offset = self.__position + offset
    elif whence == BlobReader.SEEK_END:
      offset = self.blob_info.size + offset
    self.__buffer = ""
    self.__buffer_position = 0
    self.__position = offset
    self.__eof = False
Set the file's current position, like stdio's fseek().
dataset/ETHPy150Open AppScale/appscale/AppServer/google/appengine/ext/blobstore/blobstore.py/BlobReader.seek