<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _grid_out_property(field_name, docstring):
 """Create a GridOut property."""

    def getter(self):
        self._ensure_file()

        # Protect against PHP-237
        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)