def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
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)