Get message like <filename>:<lineno>: <msg>

def flake(self, message):
        """ Get message like <filename>:<lineno>: <msg> """
        err_range = {
            'start': {'line': message.lineno - 1, 'character': message.col},
            'end': {'line': message.lineno - 1, 'character': len(self.lines[message.lineno - 1])},
        }

        severity = lsp.DiagnosticSeverity.Warning
        for message_type in PYFLAKES_ERROR_MESSAGES:
            if isinstance(message, message_type):
                severity = lsp.DiagnosticSeverity.Error
                break

        self.diagnostics.append({
            'source': 'pyflakes',
            'range': err_range,
            'message': message.message % message.message_args,
            'severity': severity
        })