# Buggy code
def buffer(self, index=None, count=None):
    """Select tab by index or url/title best match.

    Focuses window if necessary when index is given. If both index and
    count are given, use count.

    With neither index nor count given, open the qute://tabs page.

    Args:
        index: The [win_id/]index of the tab to focus. Or a substring
               in which case the closest match will be focused.
        count: The tab index to focus, starting with 1.
    """
    if count is None and index is None:
        self.openurl("qute://tabs/", tab=True)
        return

    if count is not None:
        index = str(count)

    tabbed_browser, tab = self._resolve_buffer_index(index)

    window = tabbed_browser.window()
    window.activateWindow()
    window.raise_()
    tabbed_browser.setCurrentWidget(tab)


# Traceback (ValueError)
16:39:44 DEBUG    init       app:_init_modules:468 Initializing websettings...
16:39:45 ERROR    misc       crashsignal:exception_hook:216 Uncaught exception
Traceback (most recent call last):
File "/bin/qutebrowser", line 11, in <module>
load_entry_point('qutebrowser==1.1.1', 'gui_scripts', 'qutebrowser')()
File "/usr/lib/python3.6/site-packages/qutebrowser/qutebrowser.py", line 188, in main
return app.run(args)
File "/usr/lib/python3.6/site-packages/qutebrowser/app.py", line 137, in run
init(args, crash_handler)
File "/usr/lib/python3.6/site-packages/qutebrowser/app.py", line 163, in init
_init_modules(args, crash_handler)
File "/usr/lib/python3.6/site-packages/qutebrowser/app.py", line 469, in _init_modules
websettings.init(args)
File "/usr/lib/python3.6/site-packages/qutebrowser/config/websettings.py", line 215, in init
webenginesettings.init(args)
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/webenginesettings.py", line 297, in init
websettings.init_mappings(MAPPINGS)
File "/usr/lib/python3.6/site-packages/qutebrowser/config/websettings.py", line 198, in init_mappings
mapping.set(value)
File "/usr/lib/python3.6/site-packages/qutebrowser/config/websettings.py", line 72, in set
self._set(value, settings=settings)
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/webenginesettings.py", line 154, in _set
filenames = [self._find_installed(code) for code in value]
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/webenginesettings.py", line 154, in <listcomp>
filenames = [self._find_installed(code) for code in value]
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/webenginesettings.py", line 143, in _find_installed
local_filename = spell.local_filename(code)
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/spell.py", line 64, in local_filename
all_installed = local_files(code)
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/spell.py", line 51, in local_files
for matching_dict in sorted(matching_dicts, key=version, reverse=True):
File "/usr/lib/python3.6/site-packages/qutebrowser/browser/webengine/spell.py", line 36, in version
.format(filename))
ValueError: the given dictionary file name is malformed: /usr/share/qt/qtwebengine_dictionaries/en-US.bdic

# Fixed code
def buffer(self, index=None, count=None):
    """Select tab by index or url/title best match.

    Focuses window if necessary when index is given. If both index and
    count are given, use count.

    With neither index nor count given, open the qute://tabs page.

    Args:
        index: The [win_id/]index of the tab to focus. Or a substring
               in which case the closest match will be focused.
        count: The tab index to focus, starting with 1.
    """
    if count is None and index is None:
        self.openurl("qute://tabs/", tab=True)
        return

    if count is not None:
        index = str(count)

    tabbed_browser, tab = self._resolve_buffer_index(index)

    window = tabbed_browser.widget.window()
    window.activateWindow()
    window.raise_()
    tabbed_browser.widget.setCurrentWidget(tab)