<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def ndim(self) -> int: """Get number of dimensions."""

        try:
            assert self._ndim is not None
        except (AssertionError, AttributeError):
            if len(self.variables) == 0:
                self._ndim = 0
            else:
                self._ndim = self.variables[0].ndim
        finally:
            return self._ndim