def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def enable_plugin(plugin):
    plugin = get_plugin_from_all(plugin)

    if plugin.enabled:
        flash(_("Plugin %(plugin)s is already enabled.", plugin=plugin.name),
              "info")
        return redirect(url_for("management.plugins"))

    try:
        plugin.enable()
        flash(_("Plugin %(plugin)s enabled. Please restart FlaskBB now.",
                plugin=plugin.name), "success")
    except OSError:
        flash(_("It seems that FlaskBB does not have enough filesystem "
                "permissions. Try removing the 'DISABLED' file by "
                "yourself instead."), "danger")

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