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 draw(self, context):
        layout = self.layout

        layout.template_header()

        userpref = context.user_preferences

        layout.operator_context = 'EXEC_AREA'
        layout.operator("wm.save_userpref")

        layout.operator_context = 'INVOKE_DEFAULT'

        if userpref.active_section == 'INPUT':
            layout.operator("wm.keyconfig_import")
            layout.operator("wm.keyconfig_export")
        elif userpref.active_section == 'ADDONS':
            layout.operator("wm.addon_install", icon='FILESEL')
            layout.operator("wm.addon_refresh", icon='FILE_REFRESH')
            layout.menu("USERPREF_MT_addons_online_resources")
        elif userpref.active_section == 'THEMES':
            layout.operator("ui.reset_default_theme")
            layout.operator("wm.theme_install")