python之pickle 在不同的范围内如何工作

我正在尝试从文件中获取一个 pickled 列表，但我总是出错。是否需要在每个函数内对同一文件中的同一对象进行 unpickle 操作，还是只需要 unpickle 一次就可以了？

这是我尝试的最后一件事:

import pickle, sys 
 
def openFile(fileName, mode): 
    """Open a file.""" 
 
    try: 
        file =  open(fileName, mode) 
    except IOError as e: 
        print("Unable to open the file", fileName) 
        print(e) 
        input("Press the enter key to exit.") 
        sys.exit() 
    else: 
        return file 
 
def writeScore(file, score): 
    """Write score to file.""" 
 
    try: 
        highScores = pickle.load(file) 
    except IOError as e: 
        print("File doesn't exist.") 
        print(e) 
    except EOFError as e: 
        print("File is empty.") 
        print(e) 
    else: 
        highScores.append(score) 
        highScores = highScores.sort() 
        pickle.dump(highScores, file) 
 
score_file = openFile("highScores.dat", "ab+") 
writeScore(score_file, 1000) 
score_file.close() 
 
score_file = openFile("highScores.dat", "rb") 
highScore = pickle.load(score_file) 
print(highScore) 

请您参考如下方法:

您要在打开的文件上使用 pickle.load()，而不是用于读取。此外，您的函数 openFile() 与 open() 基本相同。

我的建议:

import pickle 
 
def writeScore(file_, score): 
    """Write score to file.""" 
 
    try: 
        cache_file = open(file_, 'rb') 
    except IOError: 
        open(file_, 'a').close() 
        cache_file = open(file_, 'rb') 
 
    try: 
        highScores = pickle.load(cache_file) 
        highScores.append(score) 
        highScores.sort() 
    except EOFError: 
        highScores = [score] 
    finally: 
        cache_file.close() 
 
    writing_file = open(file_, 'wb') 
    pickle.dump(highScores, writing_file) 
    writing_file.close() 
 
def displayScores(file_): 
    """Display score from file.""" 
 
    cache_file = open(file_, 'rb') 
    try: 
        print pickle.load(cache_file) 
    except (EOFError, IOError): 
        print 'No scores to display.' 
 
if __name__ == '__main__': 
    scores_file = 'highScores.dat' 
 
    writeScore(scores_file, 2000) 
    displayScores(scores_file) 
 
    writeScore(scores_file, 1000) 
    displayScores(scores_file) 

或者，更好的是，使用 shelve。你甚至不需要这些功能:

import shelve 
 
def startDatabase(file_): 
    """Creates a shelve from file.""" 
 
    return shelve.open(file_, writeback=True) 
 
def writeScore(database, score): 
    """Write score to file.""" 
 
    try: 
        database['scores'].append(score) 
        database['scores'].sort() 
    except KeyError: 
        database['scores'] = [score] 
 
def displayScores(database): 
 
    try: 
        print database['scores'] 
    except KeyError: 
        print 'No scores to display.' 
 
if __name__ == '__main__': 
    db = startDatabase('highScores.dat') 
 
    displayScores(db) 
 
    writeScore(db, 2000) 
    displayScores(db) 
 
    writeScore(db, 1000) 
    displayScores(db) 
 
    db.close() 

两者产生相同的输出:

No scores to display. 
[1000] 
[1000, 2000]