python的各种推导式（列表推导式、字典推导式、集合推导式）

 #### 列表推导式

#!/usr/bin/python3
# -*- coding: utf-8 -*-
# @Time : 2020/11/22 14:34
# @Author : XiaoWei
# @Email : 1464819144@qq.com
# @FileName : 推导式.py
# @Project : script


# 推导式
"""
通过一行循环判断，遍历一系列数据的方式是推导式
语法： val for val in Iterable (把想要的值卸载 for的左侧)
里面是一样循环判断！根据套在推导式外层的符号判断具体是什么类型的推导式

推导式有三种：
    列表推导式: [val for val in Iterable]
    集合推导式: {val for val in Iterable}
    字典推导式: [k:v for k:v in Iterable]
"""
# 1、普通
list_a = [1, 2, 3, 4]
list_b = []
list_c = []
# 普通写法
for i in list_a:
    list_b.append(i)
print(list_b)

# 推导式写法
res = [i for i in list_a]
print(res)

# 普通修改
for i in list_a:
    i = i*2
    list_c.append(i)
print(list_c)
# 推导式写法
res = [str(i * 2) for i in list_a]
print(res)

# 2、带判断条件
list_a = [1, 2, 3, 4]
list_b = []
# 普通
for i in list_a:
    if i %2 ==0:
        list_b.append(i)
print(list_b)
# 推导式写法
res = [i for i in list_a if i % 2 == 0]
print(res)

# 3、双循环

list_a = ["a1", "a2", "a3"]
list_b = ["b1", "b2", "b3"]
list_c = []
# 常规写法
for i in list_a:
    for j in list_b:
        list_c.append(i + "  ❤❤  " + j)
print(list_c)
# 推导式写法
res = [i + "  ❤❤  " + j for i in list_a for j in list_b]
print(res)

print("<========>")
# 带有判断条件的双循环
list_a = ["a1", "a2", "a3"]
list_b = ["b1", "b2", "b3"]
# 常规写法
list_c = []
for i in list_a:
    for j in list_b:
        if list_a.index(i) == list_b.index(j):
            list_c.append(i + "  ❤❤  " + j)
print(list_c)
# 推导式写法
res = [i + "  ❤❤  " + j for i in list_a for j in list_b if list_a.index(i) == list_b.index(j)]
print(res)

 #### 字典与列表推导式

# ### 集合推导式
"""
案例:
    满足年龄在18到21,存款大于等于5000 小于等于5500的人,
    开卡格式为:尊贵VIP卡老x(姓氏),否则开卡格式为:抠脚大汉卡老x(姓氏)    
    把开卡的种类统计出来
"""
listvar = [
    {"name":"王家辉","age":18,"money":10000},
    {"name":"王水机","age":19,"money":5100},
    {"name":"王鹏","age":20,"money":4800},
    {"name":"李站","age":21,"money":2000},
    {"name":"李小龙","age":180,"money":20}
]
"""
可哈希数据:不可变数据
    Number(int float complex bool) str tuple
不可哈希数据:可变数据
    list set dict
如果是字典的键或者是集合的值,数据类型必须可哈希
"""

"""
三目运算符:
True if 条件表达式 else False
如果条件表达式成立,执行True
如果条件表达式不成立,执行False
"""

# 基本语法
setvar = set()
for i in listvar:
    if 18<=i['age']<=21 and 5000 <= i['money'] <= 5500:
        strvar = "尊贵VIP卡老" + i['name'][0]
    else:
        strvar = "抠脚大汉卡老" + i['name'][0]
    setvar.add(strvar)
print(setvar)

# 集合推导式
# lst = [15 if i % 2 == 1 else 16   for i in range(3)]# 16 15 16 例子
"""
# 分解:
{
左手边:
"尊贵VIP卡老" + i['name'][0] if 18<=i['age']<=21 and 5000 <= i['money'] <= 5500 else "抠脚大汉卡老" + i['name'][0] 
右手边:
for i in listvar
}    
"""
setvar = {"尊贵VIP卡老" + i['name'][0] if 18<=i['age']<=21 and 5000 <= i['money'] <= 5500 else "抠脚大汉卡老" + i['name'][0] for i in listvar}        
print(setvar)


# ### 字典推导式
"""
### (1)enumerate
enumerate(iterable,[start=0])
功能:枚举 ; 将索引号和iterable中的值,一个一个拿出来配对组成元组放入迭代器中
参数:
    iterable: 可迭代性数据 (常用:迭代器,容器类型数据,可迭代对象range) 
    start:  可以选择开始的索引号(默认从0开始索引)
返回值:迭代器
"""
from collections import Iterator,Iterable
listvar = ['罗淞峰',"李祥海","银燕","赖廷"]
it = enumerate(listvar)
# print(it)
# print(isinstance(it,Iterator))
# print(list(it))
"""
[里面可以是列表,元组,字符串]
(里面可以是列表,元组,字符串)
{里面是元组}
[('a',1),('b',"sdfsdfsdfsdfsd")]
(['a',1],('b',"sdfsdfsdfsdfsd"))
{('a',1),("b",909090909090909090900909)}
"""

# dict 强转迭代器变成字典
# {0: '罗淞峰', 1: '李祥海', 2: '银燕', 3: '赖廷'}
res = dict(it)
print(res)

# 字典推导式的写法变成字典
it = enumerate(listvar) # 重置迭代器
dic = {k:v for k,v in it} #k接受的是012..345 v接受的是列表中的值
print(dic)

it = enumerate(listvar,start= 10)
dic = {k:v for k,v in it}
print(dic)


### (2)zip
"""
zip(iterable, ... ...)
    功能: 将多个iterable中的值,一个一个拿出来配对组成元组放入迭代器中
    iterable: 可迭代性数据 (常用:迭代器,容器类型数据,可迭代对象range) 
返回: 迭代器

正常按照索引进行配对,放到元组中,如果找不到配对选项,直接舍弃.
"""
lst1 = ["吴波","帅乐","温素文"]
# lst2 = ["夜光花","吴耀橘","王照"]
lst2 = ["夜光花","吴耀橘","王照"]
lst3 = ["温红杰","刘璐","陈凤杰"]
it = zip(lst1,lst2,lst3)
print(it)
print(isinstance(it,Iterator))
print(list(it))

# dict强转迭代器变成字典
lst2 = ["夜光花","吴耀橘","王照"]
lst3 = ["温红杰","刘璐","陈凤杰"]
res = dict(zip(lst2,lst3))
print(res)

# 字典推导式
dic = {k:v for k,v in zip(lst2,lst3) }
print(dic)