def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def uninstall_plugin(plugin):
    plugin = get_plugin_from_all(plugin)
    if plugin.uninstallable:
        plugin.uninstall()
        Setting.invalidate_cache()

        flash(_("Plugin has been uninstalled."), "success")
    else:
        flash(_("Cannot uninstall plugin."), "danger")

    return redirect(url_for("management.plugins"))