python-3.x - 如何停止在 python 中出现此附加错误？

问题描述

我们有一个类，Message它对电子邮件消息进行建模。消息具有收件人、发件人和消息文本。该类支持以下方法：

一个构造函数，它接受发送者和接收者作为参数
append它采用一个字符串参数并将其作为新行附加到消息正文中
__str__这使得消息变成一个长字符串，如下所示：“来自：Harry Morgan\nTo：Rudolf Reindeer\n\nCome to the North Pole。”

我不断收到的错误消息在底部，我该如何解决？

这是我的代码：

class Message:
    def __init__(self,sender,recipient,message=[]):
        self.sender = sender
        self.recipient = recipient 
        self.message = message

    def append(self,message): 
        self.message=self.message.append(message)

    def __str__(self): 
        print("\nFROM: "+sender+"\n"+"TO: "+recipient+"\n\n"+self.message)
def main():
    message = []
    sender = input('Who is sending the message: ')
    recipient = input('Who would you like to send the message to: ')
    body = input('Enter body (blank line to quit): ')
    while body != '':
        message.append(body)
        body = input('Enter body (blank line to quit): ')
        if body == '':
            break
    print()
    print('FROM:', sender)
    print('TO:', recipient)
    print()
    print(*message,sep='\n') 
if __name__ == '__main__':
    main()  

An error occurred when appending a line to the message!

标签： python-3.x

你从来没有实例化你的Message类。我的意思是，您从未写过诸如message = Message(). 因此，不会发生错误。我推荐如下内容：

def main():
    sender = input('Who is sending the message: ')
    recipient = input('Who would you like to send the message to: ')

    message = Message(sender, recipient)

    body = input('Enter body (blank line to quit): ')
    while body != '':
        message.append(body)
        body = input('Enter body (blank line to quit): ')
        if body == '':
            break

    print(str(message))
if __name__ == '__main__':
    main()

你的内在之前和之前__str__都失踪了self.senderrecipient

def __str__(self):
    print("\nFROM: "+ self.sender+"\n"+"TO: "+self.recipient+"\n\n"+self.message)

目前，您的__str__方法返回None并打印字符串。如果你想要实际的字符串怎么办？stryng = str(message)不会工作，因为stryng会None
```
def __str__(self):
    return "\nFROM: "+ self.sender+"\n"+"TO: "+self.recipient+"\n\n"+self.message
```

在字符串上使用+，例如"hello world" == "hello" + ' ' +" world"是非常低效的。几乎从不这样做。改用字符串流：

import io

def __str__(self):
    with io.StringIO as ss:
        print(
            "\nFROM: ", self.sender,
            "\nTO: ", self.recipient,
            "\n\n", self.message,
            file = ss
        )
        stryng = ss.getvalue()
    return stryng

append修改“就地”。它不返回修改后的副本。

def append(self,message):
    self.message=self.message.append(message)

如果你不写一个return语句，返回什么？None

def append(self,message):
    self.message=self.message.append(message)
    return None

运算符右侧是=什么？

def append(self,message):
    self.message = None
    return None

python-3.x - 如何停止在 python 中出现此附加错误？

问题描述

解决方案

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