我发现了bug。显然，该属性的名称已从format更改为fmt，并且旧示例在其代码中显示format，当使用此属性时，处理.字典的代码不会执行，因为初始化福尔斯会返回到异常处理程序，并跳过通常执行.的其余代码
这是错误处理程序：
https://github.com/python/cpython/blob/main/Lib/logging/config.py#L670

def configure_formatter(self, config):
        """Configure a formatter from a dictionary."""
        if '()' in config:
            factory = config['()'] # for use in exception handler
            try:
                result = self.configure_custom(config)
            except TypeError as te:
                if "'format'" not in str(te):
                    raise
                #Name of parameter changed from fmt to format.
                #Retry with old name.
                #This is so that code can be used with older Python versions
                #(e.g. by Django)
                config['fmt'] = config.pop('format')
                config['()'] = factory
                result = self.configure_custom(config)

这是在result = c(**kwargs)行抛出错误的代码，因此跳过了props的处理，因为config不再包含.，因为它在第一次尝试时就从字典中弹出了！
https://github.com/python/cpython/blob/main/Lib/logging/config.py#L480

def configure_custom(self, config):
        """Configure an object with a user-supplied factory."""
        c = config.pop('()')
        if not callable(c):
            c = self.resolve(c)
        props = config.pop('.', None) # <-- removes '.' making it impossible to use it on the second try!
        # Check for valid identifiers
        kwargs = {k: config[k] for k in config if valid_ident(k)}
        result = c(**kwargs)
        if props:
            for name, value in props.items():
                setattr(result, name, value)
        return result

props = config.pop('.', None)行应该在result = c(**kwargs)之后。