AttributeError：'NoneType'對象沒有屬性'name'？

Question

我有一個問題，我無法解決。這是我的代碼：

class Person: 
    def __init__(self, name): 
    self.name = name 
    self.next = None 

class PeopleChain: 
    def __init__(self, names): 
    if names == []: 
     self.leader = None 
    else: 
     self.leader = Person(names[0]) 
     current_person = self.leader 
     for name in names[1:]: 
     current_person.next = Person(name) 
     current_person = current_person.next 
    def get_nth(self, n): 
    """Return the name of the n-th person in the chain. 
    >>> chain = PeopleChain(['a', 'b', 'c']) 
    >>> chain.get_nth(1) 
    'a' 
    """ 
    current_person = self.leader 
    for i in range(1, n): 
     if i < n: 
     current_person = current_person.next 
    return current_person.name 

當我使用chain.get_nth(4)，例如，它表明：

AttributeError: 'NoneType' object has no attribute 'name' .

這裏是我的代碼後，我改變了它：

def get_nth(self, n): 
    current_person = self.leader 
    for i in range(1, n): 
     if i < n: 
      current_person = current_person.next 
      if current_person is None: 
       raise SomeError #user-defined error 
    return current_person.name 

但它仍然不起作用。爲什麼它不起作用，我該如何解決它？非常感謝你。

Answer 1

我想你誤會了。

你PeopleChain類：

class PeopleChain: 
def __init__(self, names): 
    if names == []: 

self.leader =無 ##？

else: 
     self.leader = Person(names[0]) 
     current_person = self.leader 
     for name in names[1:]: 
      current_person.next = Person(name) 
      current_person = current_person.next 
def get_nth(self, n): 
"""Return the name of the n-th person in the chain. 
>>> chain = PeopleChain(['a', 'b', 'c']) 
>>> chain.get_nth(1) 
'a' 
""" 
current_person = self.leader 
for i in range(1, n): 
    if i < n: 
     current_person = current_person.next 
return current_person.name 

---

只是說， 型（無） 等於NoneType。除了使用

self.leader = None 

使用：

self.leader = [] 

Answer 2

嘗試而不是添加if語句，你可以加試，並抓住它更Python的方式的下面的代碼

class ShortChainError(Exception): 
    def __init__(self,*args,**kwargs): 
     Exception.__init__(self,*args,**kwargs) 

class Person: 
    def __init__(self, name): 
    self.name = name 
    self.next = None 

class PeopleChain: 
    def __init__(self, names): 
    if names == []: 
     self.leader = None 
    else: 
     self.leader = Person(names[0]) 
     current_person = self.leader 
     for name in names[1:]: 
     current_person.next = Person(name) 
     current_person = current_person.next 
    def get_nth(self, n): 
    """Return the name of the n-th person in the chain. 
    >>> chain = PeopleChain(['a', 'b', 'c']) 
    >>> chain.get_nth(1) 
    'a' 
    """ 
    current_person = self.leader 
    for i in range(1, n): 
     if i < n: 
     try: 
      current_person = current_person.next 
      name = current_person.name 
     except AttributeError: 
      raise ShortChainError("Your Message Here!!!") 
    return name 

。所以，你的代碼將成爲

if i < n: 
    try: 
     current_person = current_person.next 
     name = current_person.name 
    except AttributeError: 
     raise ShortChainError("Your Message Here!!!") 
return name 

現在在運行這段代碼這樣

PeopleChain(['a', 'b', 'c']).get_nth(4) 

這將引發自定義錯誤異常如

raise ShortChainError("Your Message Here!!!") 
__main__.ShortChainError: Your Message Here!!!