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 winding_current(pos, current, ax=0):
    """plot winding currents"""
    if ax == 0:
        ax = plt.gca()
    ax.set_title('Winding Currents / A')
    ax.grid(True)
    for p, i in zip(pos, current):
        ax.plot(p, i)