Python 存储数据

使用json.dump()和json.load()

• 先导入模块json，创建一个数字列表
• 使用文件扩展名 .json 来指出文件存储的数据为 JSON 格式
• 函数json.dump()接受两个实参：要存储的数据以及可用于存储的文件对象

# 案例：编写一个存储一组数字的简短程序，再编写一个将这些数字读取到内存中的程序，
# 第一个程序使用json.dump()来存储这组数字，第二个程序将使用json.load().
#先导入模块json
import json
numbers = [2,3,5,7,11,13]
# 使用文件扩展名 .json 来指出文件存储的数据为 JSON 格式
filename = 'numbers.json'
# 以写入模式打开这个文件，让 json 能够将数据写入其中
with open(filename,'w') as f:
    json.dump(numbers,f)
    # 使用函数json.dump()将数字列表存储到文件numbers.json中

import json
filename = 'numbers.json'
with open(filename) as f:
    numbers = json.load(f)
    # 使函数加载存储在json中的信息
print(numbers)

[2, 3, 5, 7, 11, 13]

保存和读取用户生成的数据

# 案例：存储用户的名字：
import json
username = input("What is your name? ")
filename = 'username.json'
with open(filename,'w') as f:
    json.dump(username,f)
    print("We'll remember you when you come back, " + username + '!')

What is your name? yege
We'll remember you when you come back, yege!

# 编写一个程序，向其名字被存储的用户发出问候：
# 使用json.load() 将存储在json中的信息读取到变量username中
import json
filename = 'username.json'
with open(filename) as f:
    username = json.load(f)
    print("Welocm back," + username + "!")

Welocm back,yege!

import json
filename = 'name.json'
try:
    with open(filename) as f:
        username = json.load(f)
except FileNotFoundError:
    username = input("What is your name ?")
    with open(filename,'w') as f:
        json.dump(username,f)
        print("We'll remember you when you come back, " + username + "!")
else:
    print("Welcom back, " + username + "!")

What is your name ?yege
We'll remember you when you come back, yege!

import json
filename = 'name.json'
try:
    with open(filename) as f:
        username = json.load(f)
except FileNotFoundError:
    username = input("What is your name ?")
    with open(filename,'w') as f:
        json.dump(username,f)
        print("We'll remember you when you come back, " + username + "!")
else:
    print("Welcom back, " + username + "!")

Welcom back, yege!

重构

• 将代码划分为一系列完成具体工作的函数

# 重构上面案例
import json
def greet_user():
    '''问候用户，并指出其名字'''
    filename = 'name.json'
    try:
        with open(filename) as f:
            name = json.load(f)
    except FileNotFoundError:
        name = input("What is your name ?")
        with open(filename,'w') as f:
            json.dump(name,f)
        print("We'll remembe you come bace, " + name + "!")
    else:
        print("Welcome back, " + name + "!")
greet_user()

What is your name ?qi tian da sheng sun wu kong
We'll remembe you come bace, qi tian da sheng sun wu kong!

import json
def greet_user():
    '''问候用户，并指出其名字'''
    filename = 'name.json'
    try:
        with open(filename) as f:
            name = json.load(f)
    except FileNotFoundError:
        name = input("What is your name ?")
        with open(filename,'w') as f:
            json.dump(name,f)
        print("We'll remembe you come bace, " + name + "!")
    else:
        print("Welcome back, " + name + "!")
greet_user()

Welcome back, qi tian da sheng sun wu kong!

# 重构，每个函数执行单一而清晰的任务
import json
def get_stored_name():
    '''如果存储了用户名，就获取它'''
    filename = 'name.json'
    try:
        with open(filename) as f:
            name = json.load(f)
    except FileNotFoundError:
        return None
    else:
        return name
def get_new_name():
    '''提示用户输入用户名'''
    name = input("What's your name? ")
    filename = 'name.json'
    with open(filename,'w') as f:
        json.dump(name,f)
    return name
def greet_user():
    '''问候用户，并指出其名字'''
    name = get_stored_name()
    if name :
        print("Welcom back, " + name + "!")
    else:
        name = get_new_name()
        print("We'll remember you when you come back, " + username + "!")

greet_user()
    

Welcom back, qi tian da sheng sun wu kong!

练习

1.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，再编写一个程序，从文件中读取这个值，并打印消息“I konw your favorite number! It’s____”

import json
filename = 'number.json'
number = input("我喜欢的数字是？")
with open(filename,'w') as f:
    json.dump(number,f)
    print("Thanks! I'll remember that.")

我喜欢的数字是？66
Thanks! I'll remember that.

import json
filename = 'number.json'
with open(filename) as f:
    numbers = json.load(f)
    print("I know your favorite number! It's " + numbers + "!")

I know your favorite number! It's 66!

2.记住喜欢的数字

• 将练习1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。

import json
filename = 'number.json'
try:
    with open(filename) as f:
        numbers = json.load(f)
except FileNotFoundError:
    print("该文件不存在，正在创建，请稍等！")
    number = input("我喜欢的数字是？ ")
    with open(filename,'w') as f:
        numbers = json.dump(number,f)        
else:
    print("I know your favorite number! It's " + number + "!")         

该文件不存在，正在创建，请稍等！
我喜欢的数字是？ 34

import json
filename = 'number.json'
try:
    with open(filename) as f:
        numbers = json.load(f)
except FileNotFoundError:
    print("该文件不存在，正在创建，请稍等！")
    number = input("我喜欢的数字是？ ")
    with open(filename,'w') as f:
        numbers = json.dump(number,f)        
else:
    print("I know your favorite number! It's " + number + " !") 

I know your favorite number! It's 34 !

3. 验证用户

• 在前面的案例中假设用户自己已输入用户名，要么是首次运行该程序，修改这个程序，应对这样的情形：当前和最后一次运行程序的用户并非同一个人。再greet()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

# 原代码：
import json
def get_stored_name():
    '''如果存储了用户名，就获取它'''
    filename = 'name.json'
    try:
        with open(filename) as f:
            name = json.load(f)
    except FileNotFoundError:
        return None
    else:
        return name
def get_new_name():
    '''提示用户输入用户名'''
    name = input("What's your name? ")
    filename = 'name.json'
    with open(filename,'w') as f:
        json.dump(name,f)
    return name
def greet_user():
    '''问候用户，并指出其名字'''
    name = get_stored_name()
    if name :
        print("Welcom back, " + name + "!")
    else:
        name = get_new_name()
        print("We'll remember you when you come back, " + username + "!")

greet_user()

# 修改代码：-----第一次运行，无name.json文件
import json
def get_stored_name():
    '''如果存储了用户名，就获取它'''
    filename = 'name.json'
    try:
        with open(filename) as f:
            name = json.load(f)
    except FileNotFoundError:
        return None
    else:
        return name
def get_new_name():
    '''提示用户输入用户名'''
    name = input("What's your name? ")
    filename = 'name.json'
    with open(filename,'w') as f:
        json.dump(name,f)
    return name
def greet_user():
    '''问候用户，并指出其名字'''
    name = get_stored_name()
    if name :
        choose = input("The name is yours? (YES/NO)")
        if choose == 'YES':
            print("Welcom back, " + name + "!")
        else:
            print("Please! Write The True name.")
            name = get_new_name()
    else:
        name = get_new_name()
        print("We'll remember you when you come back, " + name + "!")

greet_user()

What's your name? YeGeLi
We'll remember you when you come back, YeGeLi!

# 修改代码：-----第二次运行，确认用户，并添加用户
import json
def get_stored_name():
    '''如果存储了用户名，就获取它'''
    filename = 'name.json'
    try:
        with open(filename) as f:
            name = json.load(f)
    except FileNotFoundError:
        return None
    else:
        return name
def get_new_name():
    '''提示用户输入用户名'''
    name = input("What's your name? ")
    filename = 'name.json'
    with open(filename,'w') as f:
        json.dump(name,f)
    return name
def greet_user():
    '''问候用户，并指出其名字'''
    name = get_stored_name()
    if name :
        choose = input("The name is yours? (YES/NO)")
        if choose == 'YES':
            print("Welcom back, " + name + "!")
        else:
            print("Please! Write The True name.")
            name = get_new_name()
    else:
        name = get_new_name()
        print("We'll remember you when you come back, " + name + "!")

greet_user()

The name is yours? (YES/NO)YES
Welcom back, YeGeLi!