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 i1beta_phasor(up, i1, beta, r1, xd, xq, ax=0):
    """creates a phasor plot
    up: internal voltage
    i1: current
    beta: angle i1 vs up [deg]
    r1: resistance
    xd: reactance in direct axis
    xq: reactance in quadrature axis"""

    i1d, i1q = (i1*np.sin(beta/180*np.pi), i1*np.cos(beta/180*np.pi))
    uxdq = ((r1*i1d - xq*i1q), (r1*i1q + xd*i1d))
    __phasor_plot(ax, up, (i1d, i1q), uxdq)