# Buggy code
def _get_tab_registry(win_id, tab_id):
    """Get the registry of a tab."""
    if tab_id is None:
        raise ValueError("Got tab_id None (win_id {})".format(win_id))
    if tab_id == "current" and win_id is None:
        app = get("app")
        window = app.activeWindow()
        if window is None or not hasattr(window, "win_id"):
            raise RegistryUnavailableError("tab")
        win_id = window.win_id
    elif win_id is not None:
        window = window_registry[win_id]
    else:
        raise TypeError("window is None with scope tab!")

    if tab_id == "current":
        tabbed_browser = get("tabbed-browser", scope="window", window=win_id)
        tab = tabbed_browser.currentWidget()
        if tab is None:
            raise RegistryUnavailableError("window")
        tab_id = tab.tab_id
    tab_registry = get("tab-registry", scope="window", window=win_id)
    try:
        return tab_registry[tab_id].registry
    except AttributeError:
        raise RegistryUnavailableError("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 _get_tab_registry(win_id, tab_id):
    """Get the registry of a tab."""
    if tab_id is None:
        raise ValueError("Got tab_id None (win_id {})".format(win_id))
    if tab_id == "current" and win_id is None:
        app = get("app")
        window = app.activeWindow()
        if window is None or not hasattr(window, "win_id"):
            raise RegistryUnavailableError("tab")
        win_id = window.win_id
    elif win_id is not None:
        window = window_registry[win_id]
    else:
        raise TypeError("window is None with scope tab!")

    if tab_id == "current":
        tabbed_browser = get("tabbed-browser", scope="window", window=win_id)
        tab = tabbed_browser.widget.currentWidget()
        if tab is None:
            raise RegistryUnavailableError("window")
        tab_id = tab.tab_id
    tab_registry = get("tab-registry", scope="window", window=win_id)
    try:
        return tab_registry[tab_id].registry
    except AttributeError:
        raise RegistryUnavailableError("tab")