def __init__(self, package, version):
        """Construct a new requirement.

        :param package: the package name.
        :param version: a semver compatible version specification.
        """
        self.package = package
        self.version = version
        if self.version and not re.match(r"[<=>~]", version[:2]):
            self.version = "=={}".format(self.version)
def idq_psiq(id, iq, psiq, ax=0):
    """creates a surface plot of psiq vs id, iq"""
    if ax == 0:
        _create_3d_axis()
        ax = plt.gca()
    _plot_surface(ax, id, iq, psiq,
                  (u'Id/A', u'Iq/A', u'Psi q/Vs'),
                  azim=210)