字典(dict)

- 日理万妓 2022-06-02 04:29 362阅读 0赞

## 字典创建 ##

*  赋值创建字典
 *  通过工厂函数创建字典
 *  通过字典的 fromkeys 方法创建字典

#### 赋值创建字典 , key-value , 键值对 ####

![这里写图片描述][SouthEast]

#### 通过工厂函数创建字典 ####

![这里写图片描述][SouthEast 1]

#### 通过字典的 fromkeys 方法创建字典,所有元素有一个默认值; ####

# 如果没有指定默认值,默认为 None;
    print {}.fromkeys("hello")
    {
       'h': None, 'e': None, 'l': None, 'o': None}
    
    # 给每个元素设置默认值为 "123";
    print {}.fromkeys(["user1", "user2", "user3"], "123")
    {
       'user2': '123', 'user3': '123', 'user1': '123'}

**应用案例: 生成多个银行卡号,并初始化密码为”000000”**

# 卡号由 6 位组成, 前 3 位是 610 , 后面的依次是 001, 002, 003...10
      4 cardids = []
      5 for i in range(1,11):
      6     a = "610%.3d" %(i)
      7     cardids.append(a)
      8 print {}.fromkeys(cardids,"000000")

![这里写图片描述][SouthEast 2]

## 分析字典的特性(跟元组和列表比较) ##

**字典不能索引和切片,因为字典是无序的数据类型;**  
**字典不支持重复和连接;**  
**字典支持成员操作符: 判断字典的key值是否在字典中存在; in, not in**  
![这里写图片描述][SouthEast 3]

## 字典的增删改查 ##

### 增 ###

**- 字典名\[key\] = value**  
**- d.update(a=1, b=2)**  
**- d.update(\{‘a’:1, ‘b’,2\})**  
**- d.setdefault(‘a’, 1)**

#### 通过字典名 \[key\]=value, 将 key-value 添加到字典中 ; ####

services = {
       "ftp":[20,21]}
    
    services['http'] = [80, 8080]
    {
       'ftp': [20, 21], 'http': [80, 8080]}

#### update 方法实现添加: key 存在,覆盖 value 值, 否则,添加 ####

services = {
       "ftp":[20,21]}
    services1 = {
       'http':[80,8080]}
    services.update(services1)
    print services
    
    services.update(http=[80,8080], ftp=22)
    print services
    {
       'ftp': 22, 'http': [80, 8080]}

![这里写图片描述][SouthEast 4]

![这里写图片描述][SouthEast 5]

#### setdefault 实现添加: key 存在,不覆盖 value 值, 否则,添加 ####

services = {
       "ftp":[20,21]}
    services.setdefault("ftp", 22)
    print services
    {
       'ftp': [20, 21]}

![这里写图片描述][SouthEast 6]

### 改 ###

*  **字典名\[key\]=value**
 *  **d.update(\{‘a’:2, ‘b’:3\})**
 *  **d.update(a=2, b=3)**

![这里写图片描述][SouthEast 7]

### 查 ###

*  **查看key值;**
 *  **查看value值;**
 *  **查看key-value键值对;**
 *  **查看key是否存在;**

services = {
       'ftp': 22, 'http': [80, 8080]}
    # 查看 key 值
    services.keys()
    services.viewkeys() # 给 key 起名字
    services.iterkeys()
    
    # 查看 value 值
    services.values()
    services.viewvalues()
    
    # 查看 key-value 键值对
    services.items()
    [('ftp', 22), ('http', [80, 8080])]
    
    # 查看 key 是否存在 ;
    services.has_key('ftpp')
    
    # 查看指定 key 对应的 value 值;如果 key 不存在,不报错; 如果存在,返回 value 值;
    # services['ftp'] 如果 key 不存在,直接报错;
    services.get('ftpp')

### 删 ###

d.pop(key)      删除指定 key 的字典元素;
    d.popitem()     随机删除字典的 key-value 元素 ;
    del d[key]      删除指定 key 的字典元素;
    d.clear()       清空字典元素

### 循环遍历字典 ###

![这里写图片描述][SouthEast 8]

**\# 默认情况下遍历字典的 key 值;**  
![这里写图片描述][SouthEast 9]

### 字典应用 ###

#### 应用1: 通过字典实现case语句 ####

*  **目前python不支持case语句;**
 *  **实现case语句的两种方式:**  
    
    
     *  **if…elif…elif…else…**
     *  **字典实现**

# if...elif...elif...else... 实现:
    
      3 from __future__ import division
      4 while True:
      5     num1 = input('a:')
      6     ope = raw_input("运算符")
      7     num2 = input('b:')
      8 
      9     if ope == "+":
     10         print ("%d+%d=%d") %(num1,num2,num1+num2)
     11     elif ope == "-":
     12         print ("%d-%d=%d") %(num1,num2,num1-num2)
     13     elif ope == "*": 14 print ("%d*%d=%d") %(num1,num2,num1*num2) 15 elif ope == "/": 16 print ("%d/%d=%d") %(num1,num2,num1/num2) 17 else: 18 print "error operator"

![这里写图片描述][SouthEast 10]

# 字典实现 case 语句
      4 from __future__ import division
      5 num1 = input()
      6 ope = raw_input()
      7 num2 = input()
      8 
      9 d = {
     10     "+":num1+num2,
     11     "-":num1-num2,
     12     "*":num1*num2,
     13     "/":num1/num2
     14 }
     15 
     16 if not ope in d:
     17     print "error operator"
     18 else:
     19     print d[ope]

![这里写图片描述][SouthEast 11]

#### 应用2:用户管理系统 ####

1.注册新用户
    如果注册用户已经存在,则报错;
    需要填写信息: name, passwd, gender, email,age;
    2.用户登录 要求同之前写的用户登录系统
    3.注销用户 用户注销时,需要输入用户名和正确的用户密码
    4.显示用户信息 显示系统中存在所有已经注册用户的信息;
    5.退出系统

4 info = ''' 5 用户管理系统 6 1）注册新用户 7 2）用户登陆 8 3）注销用户 9 4）显示用户信息 10 5）退出系统 11 '''
     12 users = ['xixi']
     13 passwd = ['123']
     14 choice = raw_input(info)
     15 if choice == "1":
     16     user = raw_input("user:")
     17     if user in users:
     18         print("用户已存在")
     19     else:
     20         users.append(user)
     21         inpasswd = raw_input("passwd:")
     22         passwd.append(inpasswd)
     23         name = raw_input("name:")
     24         gender = raw_input("gender:")
     25         email = raw_input("email:")
     26 elif choice == "2":
     27     trycount = 0
     28 
     29     while trycount < 3:
     30         inuser = raw_input("user:")
     31         if inuser not in users:
     32             print ("用户不存在")
     33             exit()
     34         inpasswd = raw_input("passwd:")
     35         if inpasswd == passwd[users.index(inuser)]:
     36             print ("ok")
     37             exit()
     38         else:
     39             print("帐号密码不匹配")
     40             trycount +=1
     41     else:
     42         print "登录失败"
     43 elif choice == "3":
     44     trycount = 0
     45 
     46     while trycount < 3:
     47         inuser = raw_input("user:")
     48         if inuser not in users:
     49             print ("用户不存在")
     50             exit()
     51         inpasswd = raw_input("passwd:")
     52         if inpasswd == passwd[users.index(inuser)]:
     53             print ("ok")
     54             users.remove(inuser)
     55             passwd.pop(users.index(inuser))
     56         else:
     57             print("帐号密码不匹配")
     58             trycount +=1
     59     else:
     60         print "登录失败"
     61 elif choice == "4":
     62     print users,passwd
     63 elif choice == "5":
     64     exit()

[SouthEast]: /images/20220602/a1f1a35e1813434791337ad9e9e35453.png
[SouthEast 1]: /images/20220602/c2df28cec8084bf89235186811ecb42c.png
[SouthEast 2]: /images/20220602/6bdbfd1faf99400096e739b28b1d8285.png
[SouthEast 3]: /images/20220602/43b222d26c334dbe91431ef3e3f24fa8.png
[SouthEast 4]: /images/20220602/7696a5e510d84a099c5dd99234a2cbe3.png
[SouthEast 5]: /images/20220602/81648da2341149f5b45f836544189c7c.png
[SouthEast 6]: /images/20220602/954eabc4ccae4315913626929cbe9e2d.png
[SouthEast 7]: /images/20220602/fc069b3e3c624fa8902ae054dbe9aad6.png
[SouthEast 8]: /images/20220602/b5f1942a76c549b5ad17f241889d11c0.png
[SouthEast 9]: /images/20220602/ffd1418f855842a6a4cb851eb513b623.png
[SouthEast 10]: /images/20220602/013c986f0b364c99ba58ef1ce275ed63.png
[SouthEast 11]: /images/20220602/e9eabddca7ea4b9e8476f087398a7b84.png