Python 3：Pickling和UnPickling类实例返回“无持久加载”错误

Question

我正在尝试制作一个程序，收集大量关于乐队中某些玩家何时可以在这个圣诞节玩弄的数据，我正在努力让pickle功能做我想做的......数据存储在Player下面的类的类实例：

import pickle

class Player():
    def __init__(self, name, instrument, availability):
        self.Name=name
        self.Instrument=instrument
        self.Availability=availability

播放器列表， PlayerList被定义为一个空列表，我已经定义了一个函数AddPlayer ，它将初始化一个类实例，并将播放器的详细信息存储为属性...

PlayerList=[]

def AddPlayer(PlayerList, name, instrument, availability):
    NewPlayer = Player(name, instrument, availability)
    PlayerList.append(NewPlayer)
    print("Player "+name+" has been added.\n\n")

然后，我有一个功能，用于存储用户退出程序时的播放器列表...

def StartProgram(PlayerList):
    while True:
        choice=input("Would you like to:\n1 Add a Player?\n2 Quit?\n")

        if choice=="1":                
        ## Adds the details of the Player using the above function
            AddPlayer(PlayerList, "Test Player", "Instrument", ["1st Dec AM"])
            StartProgram(PlayerList)

        elif choice=="2":
            file=open("BuskingList.txt", "wb")
            file=open("BuskingList.txt", "ab")            
            def AddToList(PlayerList):
                print("PlayerList: "+str(PlayerList))
                HalfPlayerList=PlayerList[:5]
                ## For some reason, pickle doesn't like me trying to dump a list with more than
                ## 5 values in it, any reason for that?

                for Player in HalfPlayerList:
                    print("Player: "+str(Player))
                    PlayerList.remove(Player)
                    ## Each player removed from original list so it's only added once.

                print("HalfPlayerList: "+str(HalfPlayerList))
                pickle.dump(HalfPlayerList, file)
                if len(PlayerList) !=0:
                    AddToList(PlayerList)
                    ## Recursive function call while there are still players not dumped
            AddToList(PlayerList)
            file.close()
            quit()

        else:
            print("Enter the number 1, 2, or 3.\n")
            StartProgram(PlayerList)

最后一个函数在程序开始时运行，以加载所有玩家的信息......

def Start():
    file=open("BuskingList.txt", "rb")
    print("File contains: "+str(file.readlines()))
    PlayerList=[]
    CheckForPlayers=file.read()
    if CheckForPlayers!="":
        file=open("BuskingList.txt", "rb")
        ListOfLists=[]
        for line in file:
            ToAppend=pickle.load(file)
            ListOfLists.append(ToAppend)
        for ListOfPlayers in ListOfLists:
            for Player in ListOfPlayers:
                PlayerList.append(Player)
        StartProgram(PlayerList)


print("When entering dates, enter in the form 'XXth Month AM/PM'\n")
Start()

当程序第一次运行时（提供BuskingList.txt存在），程序运行正常，添加一个名称工作并将其腌制并在退出时将其转储显然有效。 但是，当程序重新启动时，它无法读取存储的数据，错误如下...

File contains: [b'\x80\x03]q\x00c__main__\n', b'Player\n', b'q\x01)\x81q\x02}q\x03(X\x04\x00\x00\x00Nameq\x04X\x0b\x00\x00\x00Test Playerq\x05X\n', b'\x00\x00\x00Instrumentq\x06h\x06X\x0c\x00\x00\x00Availabilityq\x07]q\x08X\n', b'\x00\x00\x001st Dec AMq\tauba.']
Traceback (most recent call last):
  File "I:/Busking/Problem.py", line 63, in <module>
    Start()
  File "I:/Busking/Problem.py", line 54, in Start
    ToAppend=pickle.load(file)
_pickle.UnpicklingError: A load persistent id instruction was encountered,
but no persistent_load function was specified.

我做了一些研究，发现这个持久的id malarkey应该不是问题，为什么它出现在这里？ 另外，为什么酸洗时列表的五个值限制？ 任何帮助，将不胜感激。

Answer 1

您首先使用.readlines()读取列表：

print("File contains: "+str(file.readlines()))

然后尝试再次阅读：

CheckForPlayers=file.read()

这不起作用; 文件指针现在位于文件的末尾。 倒带或重新打开文件：

file.seek(0)  # rewind to start

这不是你需要检查文件内容; 让pickle为你做那件事。

接下来，您逐行阅读文件：

for line in file:
    ToAppend=pickle.load(file)

这不起作用; pickle格式是二进制的 ，不是面向行的，你通过使用迭代读取 ，然后通过传入文件对象再次读取 。

将文件完全读取到pickle模块：

with open("BuskingList.txt", "rb") as infile:
    ToAppend=pickle.load(file)

你还在你的代码中提到：

## For some reason, pickle doesn't like me trying to dump a list with more than
## 5 values in it, any reason for that?

Pickle对任何列表大小没有任何问题 ，没有理由将你的玩家列表分成五个块。 您没有说明遇到的问题，但列表中的项目数量不是原因：

>>> import pickle
>>> with open('/tmp/test.pickle', 'wb') as testfile:
...     pickle.dump(range(1000), testfile)
... 
>>> with open('/tmp/test.pickle', 'rb') as testfile:
...     print len(pickle.load(testfile))
... 
1000

这存储并重新加载了1000个整数的列表。