使用Python的pickle打开并保存字典

Question

在我的intro comp sci课程的最后几天，我们开始创建词典。 我们书中的家庭作业程序要求我们创建可以查找，添加，更改和删除一组名称和电子邮件地址的内容。 它要求我们挑选字典，但对我而言，它是规定每次程序启动时，它应该从文件中检索字典并取消它。 我不知道我是否将自己编入角落，但我无法弄清楚到目前为止我是如何做到这一点的。

我的代码：

import mMyUtils
import pickle
LOOK_UP = 1
ADD = 2
CHANGE = 3
DELETE = 4
QUIT = 5

def main():
    emails = {}
    choice = 0
    while choice != QUIT:
        choice = getMenuChoice()
        if choice == LOOK_UP:
            lookUp(emails)
        elif choice == ADD:
            add(emails)
        elif choice == CHANGE:
            change(emails)
        elif choice == DELETE:
            delete(emails)
        else:
            exit

def getMenuChoice():
    print()
    print('Name and Email Address Catalog')
    print('------------------------------')
    print('1. Look up an email address')
    print('2. Add a new email address')
    print('3. Change an email address')
    print('4. Delete an email address')
    print('5. Quit the program')
    print()

    choice = int(input('Enter the choice: '))
    while choice < LOOK_UP or choice > QUIT:
        choice = int(input('Enter a valid choice: '))

    return choice

def lookUp(emails):
    name = input('Enter a name: ')
    print(emails.get(name, 'Not found.'))

def add(emails):
    name = input('Enter a name: ')
    address = input('Enter an email address: ')
    if name not in emails:
        emails[name] = address
        pickle.dump(emails, open("emails.dat", "wb"))
    else:
        print('That entry already exists.')

def change(emails):
    name = input('Enter a name: ')
    if name in emails:
        address = input('Enter the new address: ')
        emails[name] = address
        pickle.dump(emails, open("emails.dat", "wb"))
    else:
        print('That name is not found.')

def delete(emails):
    name = input('Enter a name: ')
    if name in emails:
        del emails[name]
    else:
        print('That name is not found.')

main()

我知道我应该将我的电子邮件变量设置为某种形式的pickle.load，但我无法弄清楚我的生活。 mMyUtils是我为try / except逻辑创建的库，我会把它放在一次我得到新的东西工作。

Answer 1

如果你像这样保存字典：

pickle.dump(emails, open('emails.dat', 'wb'))

以下将加载它：

emails = pickle.load(open('emails.dat', 'rb'))

Answer 2

您必须先加载文件并lookUp()数据，然后才能访问它，将lookUp()更改为：

def lookUp(emails):
    with open("emails.dat", "rb") as fo:
        emails = pickle.load(fo)

    name = input('Enter a name: ')
    print(emails.get(name, 'Not found.'))

Answer 3

考虑自己使用ast.literal_eval而不是pickle： http ：//docs.python.org/2/library/ast.html#ast.literal_eval

>>>import ast
>>> print mydict
{'bob': 1, 'danny': 3, 'alan': 2, 'carl': 40}
>>> string="{'bob': 1, 'danny': 3, 'alan': 2, 'carl': 40}"
>>> type(string)
<type 'str'>
>>> type( ast.literal_eval(string) )
<type 'dict'>

要从文件中保存/读取dict，可以像使用普通字符串一样进行。

Answer 4

问题是，我想我没有足够强调，如果字典首先不存在，我本来应该做的。 设计文档声明每次运行程序时都应加载字典。 好吧，如果你是第一次运行程序，你没有要加载的字典，导致错误。 我通过使用try / except基本上执行该功能两次来解决这个问题。

我的代码：

import mMyUtils
import pickle
import dictionaryGenerator
LOOK_UP = 1
ADD = 2
CHANGE = 3
DELETE = 4
QUIT = 5

def main():
    hasError = False
    try:
        emails = pickle.load(open('emails.dat', 'rb'))
        choice = 0
        while choice != QUIT:
            choice = getMenuChoice()
            if choice == LOOK_UP:
                lookUp(emails)
            elif choice == ADD:
                 add(emails)
            elif choice == CHANGE:
                change(emails)
            elif choice == DELETE:
                delete(emails)
            else:
                print("Good-bye!")
                exit
    except Exception as err:
        hasError = True
        mMyUtils.printError("Error: no such file",err)
        mMyUtils.writeToErrorLog()

    finally:
        if hasError:
            emails = {}
        choice = 0
        while choice != QUIT:
            choice = getMenuChoice()
            if choice == LOOK_UP:
                lookUp(emails)
            elif choice == ADD:
                add(emails)
            elif choice == CHANGE:
                change(emails)
            elif choice == DELETE:
                delete(emails)
            else:
                print("Good-bye!")
                exit





def getMenuChoice():
    print()
    print('Name and Email Address Catalog')
    print('------------------------------')
    print('1. Look up an email address')
    print('2. Add a new email address')
    print('3. Change an email address')
    print('4. Delete an email address')
    print('5. Quit the program')
    print()

    choice = int(input('Enter the choice: '))
    while choice < LOOK_UP or choice > QUIT:
        choice = int(input('Enter a valid choice: '))

    return choice

def lookUp(emails):

    name = input('Enter a name: ')
    print(emails.get(name, 'Not found.'))

def add(emails):
    name = input('Enter a name: ')
    address = input('Enter an email address: ')
    if name not in emails:
        emails[name] = address
        with open("emails.dat",  "wb") as infile:
            pickle.dump(emails, infile)

    else:
        print('That entry already exists.')

def change(emails):
    name = input('Enter a name: ')
    if name in emails:
        address = input('Enter the new address: ')
        emails[name] = address
        with open("emails.dat", "wb") as infile:
            pickle.dump(emails, infile)

    else:
        print('That name is not found.')

def delete(emails):
    name = input('Enter a name: ')
    if name in emails:
        del emails[name]
    else:
        print('That name is not found.')

main()