human
Write me a the Python program you requested given the following:
Complete the below
def _grid_out_property(field_name, docstring):

    ''''Create a GridOut property.'
    '''
assistant
#Here is the Python program you requested.
    def getter(self):
        self._ensure_file()
        if (field_name == 'length'):
            return self._file.get(field_name, 0)
        return self._file.get(field_name, None)
    docstring += '\n\nThis    attribute    is    read-only.'
    return property(getter, doc=docstring)