Python 3 : Pickling and UnPickling class instances returning "no persistent load" error

Question

我正在尝试制作一个程序，收集有关乐队中的某些玩家何时可以在今年圣诞节进行街头表演的大量数据，并且我正在努力让 pickle 函数执行我想要的操作...数据存储在以下类的类实例中，Player:

import pickle

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

玩家列表，PlayerList首先被定义为一个空列表，我定义了一个函数，AddPlayer，它将使用玩家的详细信息初始化一个类实例存储为属性...

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，可以在用户退出程序时存储玩家列表...

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()

当程序首次运行时(假设 BuskingList.txt 存在)，程序运行良好，添加名称有效，对其进行 pickle 并在退出时转储它显然有效。但是，当程序重新启动时，它无法读取存储的数据，并出现以下错误...

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 不应该成为问题，那么为什么它会出现在这里呢？另外，为什么 pickle 时列表上有五个值限制？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()

这行不通；文件指针现在位于文件末尾。快退或重新打开文件:

file.seek(0)  # rewind to start

并不是说您需要在此处检查文件内容；让 pickle 为您做这件事。

接下来逐行读取文件:

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

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

将文件的读取完全交给 pickle 模块:

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

您还在代码中提到:

## 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 对于任何列表大小都没有问题，没有理由将您的玩家列表分成五个部分。您没有说明遇到了什么问题，但列表中的项目数不可能是原因:

>>> 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。