<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_metal(self, efermi_tol=1e-4):
 """ Check if the band structure indicates a metal by looking if the fermi level crosses a band. Returns: True if a metal, False if not """

        for spin, values in self.bands.items():
            for i in range(self.nb_bands):
                if np.any(values[i, :] - self.efermi < -efermi_tol) and \
                        np.any(values[i, :] - self.efermi > efermi_tol):
                    return True
        return False