缺少2个必需的位置参数Classmethod Python

Question

对不起，我在这个问题上挣扎了很长时间。我尝试使用函数totalPayments，它使用monthlyPayment类函数，参数在初始化阶段传递。我得到一个错误，缺少2个必需的位置参数

class Loan(object):
   def __init__(self, asset, face, rate , term):
       self._asset = asset
       self._face = face
       self._rate = rate
       self._term = term

   @classmethod
   def monthlyPayment(cls,face,rate,term,period=None):
       return ((rate*face*((1+rate)**term)))/(((1+rate)**term)-1)

   def totalPayments(self):
       return (self.monthlyPayment(self) * self._term) 

l = Loan(None,1000,0.025,10)
print(l.totalPayments()) # gets an error missing 2 required positional arguments

Answer 1

您正在从实例（self）调用monthlyPayment，并且没有为face、rate和{}提供参数。在

它也不应该是类方法，因为您使用实例的属性：

class Loan(object):
   def __init__(self, asset, face, rate , term):
       self._asset = asset
       self._face = face
       self._rate = rate
       self._term = term

   def monthlyPayment(self, period=None):
       return ((self._rate*self._face*((1+self._rate)**self._term)))/(((1+self._rate)**self._term)-1)

   def totalPayments(self):
       return (self.monthlyPayment() * self._term)

Answer 2

您得到的堆栈错误是：

Traceback (most recent call last):
  File "C:/Users/cd00119621/PycharmProjects/ideas/stackoverflow.py", line 16, in <module>
    print(l.totalPayments())
  File "C:/Users/cd00119621/PycharmProjects/ideas/stackoverflow.py", line 13, in totalPayments
    return (self.monthlyPayment(self) * self._term)
TypeError: monthlyPayment() missing 2 required positional arguments: 'rate' and 'term'

这里的线索是monthlyPayment()方法给出了缺少2个参数的错误。此方法需要传递3个参数（不包括self），第4个参数是可选的。在

def monthlyPayment(cls,face,rate,term,period=None):

但是当你从你的totalPayments方法调用它时，你只传递了一个参数self。在

return (self.monthlyPayment(self) * self._term)

您不需要传递self，它将自动传递，因此您需要传递其他3个预期的参数face,rate,term