# Buggy code
def yank(self, what="url", sel=False, keep=False):
    """Yank something to the clipboard or primary selection.

    Args:
        what: What to yank.

            - `url`: The current URL.
            - `pretty-url`: The URL in pretty decoded form.
            - `title`: The current page's title.
            - `domain`: The current scheme, domain, and port number.
            - `selection`: The selection under the cursor.

        sel: Use the primary selection instead of the clipboard.
        keep: Stay in visual mode after yanking the selection.
    """
    if what == "title":
        s = self._tabbed_browser.page_title(self._current_index())
    elif what == "domain":
        port = self._current_url().port()
        s = "{}://{}{}".format(
            self._current_url().scheme(),
            self._current_url().host(),
            ":" + str(port) if port > -1 else "",
        )
    elif what in ["url", "pretty-url"]:
        s = self._yank_url(what)
        what = "URL"  # For printing
    elif what == "selection":

        def _selection_callback(s):
            if not s:
                message.info("Nothing to yank")
                return
            self._yank_to_target(s, sel, what, keep)

        caret = self._current_widget().caret
        caret.selection(callback=_selection_callback)
        return
    else:  # pragma: no cover
        raise ValueError("Invalid value {!r} for `what'.".format(what))

    self._yank_to_target(s, sel, what, keep)


# 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 yank(self, what="url", sel=False, keep=False):
    """Yank something to the clipboard or primary selection.

    Args:
        what: What to yank.

            - `url`: The current URL.
            - `pretty-url`: The URL in pretty decoded form.
            - `title`: The current page's title.
            - `domain`: The current scheme, domain, and port number.
            - `selection`: The selection under the cursor.

        sel: Use the primary selection instead of the clipboard.
        keep: Stay in visual mode after yanking the selection.
    """
    if what == "title":
        s = self._tabbed_browser.widget.page_title(self._current_index())
    elif what == "domain":
        port = self._current_url().port()
        s = "{}://{}{}".format(
            self._current_url().scheme(),
            self._current_url().host(),
            ":" + str(port) if port > -1 else "",
        )
    elif what in ["url", "pretty-url"]:
        s = self._yank_url(what)
        what = "URL"  # For printing
    elif what == "selection":

        def _selection_callback(s):
            if not s:
                message.info("Nothing to yank")
                return
            self._yank_to_target(s, sel, what, keep)

        caret = self._current_widget().caret
        caret.selection(callback=_selection_callback)
        return
    else:  # pragma: no cover
        raise ValueError("Invalid value {!r} for `what'.".format(what))

    self._yank_to_target(s, sel, what, keep)