python 之列表推导式

#推导式：可以实现一些简单的操作，重要是代码比较简洁 通过一行循环判断,遍历一系列数据的方式是推导式
#语法： var for val in Iterable(把想要的值写在for的左侧)
#里面是一行循环判断，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

#语法： var for val in Iterable(把想要的值写在for的左侧）
#列表推导式: [val for val in Iterable]

# lst = [1,2,3,4,5,6,7,8,9,10]
lst = []
for i in range(1,11):
    lst.append(i)    
print(lst)

# (1).普通列表推导式
lst = [i for i in range(1,11)]
print(lst)

# [1,2,3,4] => 2,4,6,8
lst = [i * 2 for i in range(1,5)]
print(lst)

# (2) 带有判断条件的列表推导式
'''
推导式后面跟着的只能是单项分支，其他的是不行的
'''
# 基本写法
lst = [1,2,3,4,5,6,67,7,8,9]
lst2 = []
for i in lst:
    if i % 2 ==1:
        lst2.append(i)
print(lst2)
# 推导式写法
lst2 = [i for i in lst if i % 2 ==1]
print(lst2)
# (3) 双循环的列表推导式
lst1 = ['a',"b","c"]
lst2 = ["d","e","f"]
# "谁♥♥谁"
lst = []
for i in lst1:
    for j in lst2:
        strvar = i + "♥♥" + j
        lst.append(strvar)
# print(lst)

lst = [i + "♥♥" + j for i in lst1 for j in lst2]
print(lst)

# (4) 带有判断条件的双循环列表推导式
lst1 = ['a',"b","c"]
lst2 = ["d","e","f"]
lst = []
for i in lst1:
    for j in lst2:
　　　　#让相索引的值进行配对
        if lst1.index(i) == lst2.index(j):
            strvar = i + "♥♥" + j
            lst.append(strvar)
print(lst)

res = [i + "♥♥" + j for i in lst1 for j in lst2 if lst1.index(i) == lst2.index(j)]
print(res)

#输出
#['a♥♥d', 'b♥♥e', 'c♥♥f']