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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _parse_options(self, options):
 """Parse the command's options. Arguments: options (dict):
 Options with which the command was called. Raises: CommandError, if a user matching the provided username does not exist. """

        for key in ('username', 'client_name', 'client_id', 'client_secret', 'trusted', 'logout_uri'):
            value = options.get(key)
            if value is not None:
                self.fields[key] = value

        username = self.fields.pop('username', None)
        if username is not None:
            try:
                user_model = get_user_model()
                self.fields['user'] = user_model.objects.get(username=username)
            except user_model.DoesNotExist:
                raise CommandError("User matching the provided username does not exist.")

        # The keyword argument 'name' conflicts with that of `call_command()`. We instead
        # use 'client_name' up to this point, then swap it out for the expected field, 'name'.
        client_name = self.fields.pop('client_name', None)
        if client_name is not None:
            self.fields['name'] = client_name

        logout_uri = self.fields.get('logout_uri')

        if logout_uri:
            try:
                URLValidator()(logout_uri)
            except ValidationError:
                raise CommandError("The logout_uri is invalid.")