code: def open_file(self, store=current_store, use_seek=False):
          
          if not isinstance(store, Store):
              raise TypeError('store must be an instance of '
                              'sqlalchemy_imageattach.store.Store, not ' +
                              repr(store))
  
          if Session.object_session(self) is None:
              try:
                  file = self.file
              except AttributeError:
                  raise IOError('no stored original image file')
              return ReusableFileProxy(file)
  
          return store.open(self, use_seek)
docs: Opens the file-like object which is a context manager
          (that means it can used for :keyword:`with` statement).
  
          If ``use_seek`` is :const:`True` (though :const:`False` by default)
          it guarentees the returned file-like object is also seekable
          (provides :meth:`~file.seek()` method).
  
          :param store: the storage which contains image files.
                        :data:`~sqlalchemy_imageattach.context.current_store`
                        by default
          :type store: :class:`~sqlalchemy_imageattach.store.Store`
          :returns: the file-like object of the image, which is a context
                    manager (plus, also seekable only if ``use_seek``
                    is :const:`True`)
          :rtype: :class:`file`,
                  :class:`~sqlalchemy_imageattach.file.FileProxy`,
                  file-like object