如何修复错误：“AttributeError：'str'对象没有属性'make_lab'”？

Question

这是我的代码：

class Student(): 
    exam_max=None 
    lab_max=None 
    lab_num=None 
    k=None 
    students=[] 
    labs=None 
    exam=None 

    def __init__(self, name=None, conf=None): 
     keys = conf.keys() 
     self.name=name 
     self.students.append({"name":self.name, "labs":[], "exam":0}) 
     if 'exam_max' in keys: 
      self.exam_max = conf['exam_max'] 
     if 'lab_max' in keys: 
      self.lab_max = conf['lab_max'] 
     if 'lab_num' in keys: 
      self.lab_num = conf['lab_num'] 
     if 'k' in keys: 
      self.k = conf['k'] 

    def make_lab(self, m=None, n=None): 
     self.m = m 
     self.n = n 
     for i in self.students: 
      for k,v in i.iteritems(): 
       if v == self.name: 
        if len(i.get("labs"))<self.lab_num: 
         while len(i.get("labs"))<self.lab_num: 
          i.get("labs").append(0) 
     if self.n==None: 
      for i in self.students: 
       for k,v in i.iteritems(): 
        if v == self.name: 
         for b in range(len(i.get("labs"))): 
          if i.get("labs")[b]==0: 
           if self.m>=self.lab_max: 
            i.get("labs")[b]=self.lab_max 
            break 
           else: 
            i.get("labs")[b]=self.m 
            break 
     elif self.n>=0 and self.n<=self.lab_num-1: 
      for i in self.students: 
       for k,v in i.iteritems(): 
        if v == self.name: 
         for b in range(len(i.get("labs"))): 
          if b==self.n: 
           if self.m>=self.lab_max: 
            i.get("labs")[b]=self.lab_max 
           else: 
            i.get("labs")[b]=self.m 
     for i in self.students: 
      for k,v in i.iteritems(): 
       if v == self.name: 
        labs=i.get("labs") 
        exam=i.get("exam")  
     return "labs: {}, exam: {}".format(" ".join(str(v) for v in labs), str(exam))      

    def make_exam(self, m=0): 
     self.m_e=m 

     for i in self.students: 
      for k,v in i.iteritems(): 
       if v == self.name: 
        if self.m_e>=self.exam_max: 
         i["exam"]=self.exam_max 
        else: 
         i["exam"]=self.m_e 

     for i in self.students: 
      for k,v in i.iteritems(): 
       if v == self.name: 
        labs=i.get("labs") 
        exam=i.get("exam")  
     return "labs: {}, exam: {}".format(" ".join(str(v) for v in labs), str(exam)) 

    def is_certified(self): 
     for i in self.students: 
      for k,v in i.iteritems(): 
       if v == self.name: 
        rez=sum(i.get("labs"))+i.get("exam") 

      return (rez, (rez/100)>=self.k,) 

     return None 

如果方法调用是在一个做，所有的工作：

>>> oleg.make_lab(1) 
'labs: 1 0 0 0 0 0 0 0 0 0, exam: 0' 

但是：

>>> oleg.make_lab(1).make_lab(8,0).make_lab(1).make_lab(10,7).make_lab(4,1).make_lab(5).make_lab(6.5).make_exam(32) 

Traceback (most recent call last): 
    File "<pyshell#40>", line 1, in <module> 
oleg.make_lab(1).make_lab(8,0).make_lab(1).make_lab(10,7).make_lab(4,1).make_lab(5).make_lab(6.5).make_exam(32) 
AttributeError: 'str' object has no attribute 'make_lab' 

Answer 1

oleg是Student型的，因此它有方法make_lab。 方法make_lab返回一个字符串，而不是Student类型 - 因此它没有make_lab方法。

Answer 2

方法make_lab()返回一个字符串值，我们可以在方法声明中看到。
你试图实现的东西是经典的方法链接。
在你的情况下，第一次调用make_lab()方法（在oleg.make_lab(1).make_lab(8,0).....内）将返回一个字符串，但第二个连续调用自然会抛出AttributeError: 'str' object has no attribute 'make_lab'。
要构建一个方法调用链 - 链中的所有方法必须返回self（当前实例）。

... 

def make_lab(self, m=None, n=None): 
    ... 
    print("labs: {}, exam: {}".format(" ".join(str(v) for v in labs), str(exam))) 
    return self 

https://en.wikipedia.org/wiki/Method_chaining