#!/usr/bin/python3
# -*- coding: utf-8 -*-
# @Time : 2020/11/22 14:34
# @Author : XiaoWei
# @Email : [email protected]
# @FileName : 推導式.py
# @Project : script


# 推導式
"""
通過一行迴圈判斷，遍歷一系列資料的方式是推導式
語法： val for val in Iterable (把想要的值解除安裝 for的左側)
裡面是一樣迴圈判斷！根據套在推導式外層的符號判斷具體是什麼型別的推導式

推導式有三種：
    列表推導式: [val for val in Iterable]
    集合推導式: {val for val in Iterable}
    字典推導式: [k:v for k:v in Iterable]
 
"""
# 1、普通
list_a = [1, 2, 3, 4]
list_b = []
list_c = []
# 普通寫法
for i in list_a:
    list_b.append(i)
print(list_b)

# 推導式寫法
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)
# 推導式寫法
res = [str(i * 2) for i in list_a]
print(res)

# 2、帶判斷條件
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)
# 推導式寫法
res = [i for i in list_a if i % 2 == 0]
print(res)

# 3、雙迴圈

list_a = ["a1", "a2", "a3"]
list_b = ["b1", "b2", "b3"]
list_c = []
# 常規寫法
for i in list_a:
    for j in list_b:
        list_c.append(i + "  ❤❤  " + j)
 
print(list_c)
# 推導式寫法
res = [i + "  ❤❤  " + j for i in list_a for j in list_b]
print(res)

print("<========>")
# 帶有判斷條件的雙迴圈
list_a = ["a1", "a2", "a3"]
list_b = ["b1", "b2", "b3"]
# 常規寫法
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)
# 推導式寫法
res = [i + "  ❤❤  " + j for i in list_a for j in list_b if list_a.index(i) == list_b.index(j)]
print(res)