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 toggle_comment(self):
        "Toggle the selected comment tree between visible and hidden"

        current_index = self.nav.absolute_index
        self.content.toggle(current_index)

        # This logic handles a display edge case after a comment toggle. We
        # want to make sure that when we re-draw the page, the cursor stays at
        # its current absolute position on the screen. In order to do this,
        # apply a fixed offset if, while inverted, we either try to hide the
        # bottom comment or toggle any of the middle comments.
        if self.nav.inverted:
            data = self.content.get(current_index)
            if data['hidden'] or self.nav.cursor_index != 0:
                window = self._subwindows[-1][0]
                n_rows, _ = window.getmaxyx()
                self.nav.flip(len(self._subwindows) - 1)
                self.nav.top_item_height = n_rows