求助：TypeError报错——MeComCommon._set()缺少必需参数'self'

问题代码与报错 #

定义的类方法 #

@classmethod
def set_parameter(self, value, parameter_name=None, parameter_id=None, *args, **kwargs):
    """
    Set the new value of a parameter given by name or id.
    Returns success.
    :param value:
    :param parameter_name:
    :param parameter_id:
    :param args:
    :param kwargs:
    :return: bool
    """
    # get the query object
    vs = self._set(value=value, parameter_id=parameter_id, parameter_name=parameter_name, *args, **kwargs)

    # check if value setting has succeeded
    #
    # Not necessary as we get an acknowledge response or Value is out of range
    # exception when an invalid value was passed. 
    # current implementation also often fails due to rounding, e.g. setting 1.0
    # but returning 0.999755859375 when performing a self.get_parameter
    # value_set = self.get_parameter(parameter_id=parameter_id, parameter_name=parameter_name, *args, **kwargs)

    # return True if we got an ACK
    return type(vs.RESPONSE) == ACK

调用方式 #

mcc = mecom.MeComCommon()
mcc.set_parameter(value=-40, parameter_id=3000)

报错信息 #

Traceback (most recent call last):
  File "C:\Users\Michal\Desktop\THERMAL ELEPHANT V3 TEST JIG\Python Script\main.py", line 189, in <module>
    mcc.set_parameter(value=-40, parameter_id=3000)
  File "C:\Users\Michal\Desktop\THERMAL ELEPHANT V3 TEST JIG\Python Script\mecom\mecom.py", line 659, in set_parameter
    vs = self._set(value=value, parameter_id=parameter_id, parameter_name=parameter_name, *args, **kwargs)
TypeError: MeComCommon._set() missing 1 required positional argument: 'self'

问题原因 #

set_parameter被标记为@classmethod类方法，类方法的第一个参数实际是类本身（通常命名为cls），但你这里用了self作为参数名。当你通过实例mcc调用这个类方法时，传入的self其实是MeComCommon类，而非实例对象。而_set是实例方法，必须接收实例作为第一个参数，直接用类调用_set就会缺少必要的实例参数，触发报错。

解决方案 #

将set_parameter的@classmethod装饰器移除，改成普通的实例方法，这样self就会指向调用该方法的实例对象，调用self._set时就能正确传递实例参数：

def set_parameter(self, value, parameter_name=None, parameter_id=None, *args, **kwargs):
    """
    Set the new value of a parameter given by name or id.
    Returns success.
    :param value:
    :param parameter_name:
    :param parameter_id:
    :param args:
    :param kwargs:
    :return: bool
    """
    # get the query object
    vs = self._set(value=value, parameter_id=parameter_id, parameter_name=parameter_name, *args, **kwargs)

    # check if value setting has succeeded
    #
    # Not necessary as we get an acknowledge response or Value is out of range
    # exception when an invalid value was passed. 
    # current implementation also often fails due to rounding, e.g. setting 1.0
    # but returning 0.999755859375 when performing a self.get_parameter
    # value_set = self.get_parameter(parameter_id=parameter_id, parameter_name=parameter_name, *args, **kwargs)

    # return True if we got an ACK
    return type(vs.RESPONSE) == ACK

如果业务上必须保留set_parameter为类方法，需要确保_set也被定义为类方法，或者在set_parameter内部先创建实例再调用_set，但这种方式不符合你当前的调用逻辑，因此优先推荐第一种方案。

内容的提问来源于stack exchange，提问作者TeshE