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 torque_fft(order, torque, ax=0):
    """plot torque harmonics"""
    unit = 'Nm'
    scale = 1
    if np.min(torque) < -9.9e3 or np.max(torque) > 9.9e3:
        scale = 1e-3
        unit = 'kNm'
    if ax == 0:
        ax = plt.gca()
    ax.set_title('Torque Harmonics / {}'.format(unit))
    ax.grid(True)

    try:
        bw = 2.5E-2*max(order)
        ax.bar(order, [scale*t for t in torque], width=bw, align='center')
        ax.set_xlim(left=-bw/2)
    except ValueError:  # empty sequence
        pass