78、存储数据课后习题

10-11喜欢的数字 ：编写一个程序，提示用户输入他喜欢的数字，并使用json.dump() 将这个数字存储到文件中。

# -*- coding: utf-8 -*-
import  json

# 存储用户喜欢的数字
filename = "number.json"
number = raw_input("What is your favorite number: ")
with open(filename,"w") as f_obj:
    json.dump(number,f_obj)

print("Write success!")

结果：

What is your favorite number: 23
Write success!

Process finished with exit code 0

再编写一个程序，从文件中读取这个值，并打印消息“I know your favorite number! It's _____.”。

# -*- coding: utf-8 -*-
import  json

# 读取用户喜欢的数字
filename = "number.json"
with open(filename) as f_obj:
    number = json.load(f_obj)
print("I know your favorite number!It's " + number + ".")

结果：

I know your favorite number!It's 23.

Process finished with exit code 0

10-12记住喜欢的数字 ：将练习10-11中的两个程序合而为一。如果存储了用户喜欢的数字，就向用户显示它，否则提示用户输入他喜欢的数字并将其存储到文件中。
运行这个程序两次，看看它是否像预期的那样工作。
方法一：

# -*- coding: utf-8 -*-
import  json
# 如果以前存储有数字，就读取它
# 否则，提示用户输入它喜欢的数字并存储
filename = "number.json"
try:
    with open(filename) as f_obj:
        number = json.load(f_obj)
except IOError:
    number = raw_input("What is your favorite number: ")
    with open(filename,"w") as f_obj:
        json.dump(number,f_obj)
else:
    print("I know your favorite number!It's " + number + ".")

第一次运行结果：

What is your favorite number: 2323

Process finished with exit code 0

第二次运行结果：

I know your favorite number!It's 2323.

Process finished with exit code 0

方法二：

# -*- coding: utf-8 -*-
import  json
def get_number():
    """如果存储了数字，获取它"""
    filename = "number.json"
    try:
        with open(filename) as f_obj:
            number = json.load(f_obj)
    except IOError:
        return None
    else:
        return number

def write_number():
    """提示用户输入喜欢的数字"""
    filename = "number.json"
    number = raw_input("What is your favorite number: ")
    with open(filename,"w") as f_obj:
        json.dump(number,f_obj)
        return number

def print_number():
    """打印用户喜欢的数字"""
    number = get_number()
    if number:
        print("I know your favorite number!It's " + number + ".")
    else:
        number = write_number()
        print("I'll keep in mind that your favorite number is " + number)

print_number()

第一次运行结果：

What is your favorite number: 2323
I'll keep in mind that your favorite number is 2323

Process finished with exit code 0

第二次运行结果：

I know your favorite number!It's 2323.

Process finished with exit code 0

10-13验证用户 ：最后一个remember_me.py版本假设用户要么已输入其用户名，要么是首次运行该程序。我们应修改这个程序，以应对这样的情形：当前和最后一次运行该程序的用户并非同一个人。
为此，在greet_user() 中打印欢迎用户回来的消息前，先询问他用户名是否是对的。如果不对，就调用get_new_username() 让用户输入正确的用户名。
代码如下：

# -*- coding: utf-8 -*-
import json
def get_stored_username():
    """如果存储了用户名，就获取它"""
    filename = "username.json"
    try:
        with open(filename) as f_obj:
            username = json.load(f_obj)
    except IOError:
        return None
    else:
        return username
def get_new_username():
    """提示用户输入用户名"""
    username = raw_input("What is your name: ")
    filename = "username.json"
    with open(filename,'w') as f_obj:
        json.dump(username,f_obj)
        return  username
def greet_user():
    """问候用户，并指出其名字"""
    username = get_stored_username()
    if username:
        self_name = raw_input(username + " is your name?(yes/ no)\n ")
        if self_name == "yes":
            print("Welcome back, " + username + "!")
        else:
            username = get_new_username()
            print("I'll remember you when you come back, " + username + "!")
    else:
        username = get_new_username()
        print("I'll remember you when you come back, " + username + "!")

greet_user()

验证代码：

What is your name: leilei
I'll remember you when you come back, leilei!

Process finished with exit code 0

leilei is your name?(yes/ no)
 no
What is your name: 23
I'll remember you when you come back, 23!

Process finished with exit code 0

23 is your name?(yes/ no)
 yes
Welcome back, 23!

Process finished with exit code 0