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 mmf_fft(f, title='', mmfmin=1e-2, ax=0):
    """plot winding mmf harmonics"""
    if ax == 0:
        ax = plt.gca()
    if title:
        ax.set_title(title)
    else:
        ax.set_title('MMF Harmonics')
    ax.grid(True)
    order, mmf = np.array([(n, m) for n, m in zip(f['nue'],
                                                  f['mmf_nue']) if m > mmfmin]).T
    try:
        markerline1, stemlines1, _ = ax.stem(order, mmf, '-.', basefmt=" ",
                                             use_line_collection=True)
        ax.set_xticks(order)
    except ValueError:  # empty sequence
        pass