def install_pip(self, package, save=True, save_dev=False):
        """Installs a pip package.

        :param save: if `True`, pins the package to the Hydrogen requirements
            YAML file.
        :param save_dev: if `True`, pins the package as a development
            dependency to the Hydrogen requirements YAML file.
        :param return: a **single** :class:`Requirement` object, representing
            the installed version of the given package.
        """
        requirement = Requirement.coerce(package)
        click.echo("pip install " + requirement.package)
        cmd = envoy.run("pip install {}".format(str(requirement)))
        if cmd.status_code == 0:
            installed_packages = get_installed_pypackages()
            package = installed_packages[requirement.package]
            requirement.version = "=={}".format(package.version)
            if save:
                self.requirements["all"].add(requirement)
            if save_dev:
                self.requirements["dev"].add(requirement)
            if save or save_dev:
                self.requirements.save()
            return requirement
        else:
            fatal(cmd.std_err)
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