def lookup_icons(self):
        """Search for the icons corresponding to the commands to execute."""
        if self.default_icon is not None:
            if not os.path.isfile(self.default_icon):
                # if the default icon provided is not found, switch to
                # text mode
                self.default_icon = None
        for name in self.progs_name:
            self._lookup_icon(name)
Search for the icons corresponding to the commands to execute.
libqtile/widget/launchbar.py