已安装内容类对象打印

Question

我正在尝试建立一个简单的数据库学生(姓名和年龄)。当我尝试删除一个选课学生并打印数据库时，它会打印<class '__main__.data_base'>，但如果我试图删除一个非选课学生，它会很好地打印数据库。

import pickle
class data_base:
    data={}
    class __metaclass__(type):
        def __iter__(self):
            for attr in dir(data_base):
                if not attr.startswith("__"):
                    yield attr

    def __init__(self):
        self.write("")

    def write(self,my_data):
        pickle.dump( my_data, open( "database.p", "wb" ) )

    def read(self):
        return pickle.load( open( "database.p", "rb" ) )
    def delete_student(self):
        #delete key and value
        to_delete=raw_input("who do you want to delete? ")
        my_data=self.read()
        if to_delete in my_data.__iter__():
            my_data.pop(to_delete)
            self.write(data_base)
        else:
            print "no such student"

    def clear_data_base(self):
        #delete data baase
        self.write("")

def main():
    first_data={"ben":10,"dan":6}
    my_data_base=data_base()
    my_data_base.clear_data_base()
    my_data_base.write(first_data)
    print my_data_base.read()
    my_data_base.delete_student()
    print my_data_base.read()

Answer 1

问题出在这里：

self.write(data_base)

您已将类对象，而不是读取到my_data中的实例进行了pickled。将您的方法更改为

def delete_student(self):
    #delete key and value
    to_delete=raw_input("who do you want to delete? ")
    my_data=self.read()
    if to_delete in my_data.__iter__():
        my_data.pop(to_delete)
        self.write(my_data)
    else:
        print "no such student"