CODEWITHSUNDEEP
pythonclass-method
demalegabi
demalegabi

Reputation: 607

in python what happens when an instance of a class calls a @classmethod

so I have a class Model and inside model I have a method save

def save(self):
    args = list(map(self.getValueOrDefault,self.__fields__))
    args.append(self.getValueOrDefault(self.__primary_key__))
    logging.debug('saving %s' % str(args))
    row = yield from execute(self.__insert__,args)
    if row != 1:
        logging.debug('failed to insert record: affected rows: %s' % row)
    else:
        logging.info('insertion was succesful')

here is the code for getValueOrDefault, they are in the same class

def getValueOrDefault(self,key):
    value = getattr(self,key)
    if value is None:
        field = self.__mapping__[key]
        if field.default is not None:
            value = field.default() if callable(field.default) else field.default
            logging.info('using default value for %s ==> %s' % (key,value))
            setattr(self,key,value)
    return value

if I add classmethod to save and call save from an instance I get an error saying getValueOrDefault requires additional positional argument 'key'. My guess is when I call it from a instance the self (which becomes a cls) is the class itself not the instance created and I'm trying to do Model.getValueOrDefault but shouldn't it give me some error that tells me I can't call a function without initializing the class?

Upvotes: 0

Views: 113

Answers (1)

user2357112
user2357112

Reputation: 280544

My guess is when I call it from a instance the self (which becomes a cls) is the class itself not the instance created

Yup.

and I'm trying to do Model.getValueOrDefault but shouldn't it give me some error that tells me I can't call a function without initializing the class?

Nope. It's entirely valid to call Model.getValueOrDefault, but you have to pass self explicitly when you do that.

Upvotes: 1

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