如何在設計新類時打印聯繫人列表的內容

Question

我正在學習和嘗試Python。如何在我的第二個功能print_contacts中通過contact_list以便它可以打印contact_list的名稱？我確信我做錯了什麼，誰能解釋爲什麼這樣？

class Contact(object): 
    contact_list = [] 

    def __init__(self, name, email): 
     self.name = name 
     self.email = email 
     return Contact.contact_list.append(self) 

# How to pass contact_list to below function? 

    def print_contacts(contact_list): 
     for contact in contact_list: 
      print(contact.name) 

Answer 1

class Contact(object): 
    contact_list = [] 

    def __init__(self, name, email): 
     self.name = name 
     self.email = email 
     Contact.contact_list.append(self) 

    @classmethod 
    def print_contacts(cls): 
     for contact in cls.contact_list: 
      print(contact.name) 

cont1 = Contact("John", "john@john.com") 
cont2 = Contact("Mary", "mary@mary.com") 
Contact.print_contacts() 

將打印

>>John 
    Mary 

要回答你的問題，爲什麼你的代碼目前不工作：第一，你的的init方法不需要回電話，init被調用來創建對象來建立對象變量，並且通常不需要返回任何東西（特別是在這種情況下，因爲.append（）不提供任何返回值）。其次，類方法似乎更適合你正在嘗試用第二個方法做，你可以閱讀更多有關在這裏：What are Class methods in Python for?

Answer 2

對我來說沒有任何意義，有Contact對象還自己一個contact_list屬性，如果是全班級而不是實例化，則屬性更少。我會做這個：

class Contact(object): 
    def __init__(self, name, email): 
     self.name = name 
     self.email = email 

    def __str__(self): 
     return f"{self.name} <{self.email}>" 
     # or "{} <{}>".format(self.name, self.email) in older versions of 
     # python that don't include formatted strings 


contacts = [] 

def print_contacts(contacts: "list of contacts") -> None: 
    for c in contacts: 
     print(c) 

adam = Contact("Adam Smith", "adam@email.com") 
contacts.append(adam) 

bob = Contact("Bob Jones", "bob@email.com") 
contacts.append(bob) 

charlie = Contact("Charlie Doe", "charlie@email.com") 
contacts.append(charlie) 

print_contacts(contacts) 
# Adam Smith <adam@email.com> 
# Bob Jones <bob@email.com> 
# Charlie Doe <charlie@email.com> 

或者，模型的AddressBook知道如何創建Contact對象，並顯示它們。

class AddressBook(list): 
    def add_contact(self, *args, **kwargs): 
     new_contact = Contact(*args, **kwargs) 
     self.append(new_contact) 

    def display_contacts(self): 
     for contact in self: 
      print(contact) 

contacts = AddressBook() 
contacts.add_contact("Adam Smith", "adam@email.com") 
contacts.add_contact("Bob Jones", "bob@email.com") 
contacts.add_contact("Charlie Doe", "charlie@email.com") 
contacts.display_contacts()