def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def demag(isa, ax=0):
    """plot demag of NC/I7/ISA7 model
    Args:
      isa: Isa7/NC object
    """
    emag = [e for e in isa.elements if e.is_magnet()]
    demag = np.array([e.demagnetization(isa.MAGN_TEMPERATURE) for e in emag])
    _contour(ax, f'Demagnetization at {isa.MAGN_TEMPERATURE} °C',
             emag, demag, '-H / kA/m', isa)
    logger.info("Max demagnetization %f", np.max(demag))