'Prefixes all items in the completer model with the current
already done completion to enable the completion of multiple keywords.'

def update_completer_prefix(self, filter):

    prefix = str(self.completer.completionPrefix())
    if ((not prefix.endswith('    ')) and ('    ' in prefix)):
        (prefix, _) = prefix.rsplit('    ', 1)
        items = [((prefix + '    ') + item) for item in self.original_completer_items]
    else:
        items = self.original_completer_items
    old = list(map(str, self.completer_model.stringList()))
    if (set(old) != set(items)):
        self.completer_model.setStringList(items)
