列表推导式和字典推导式是什么？

它们是可以轻松创建字典和列表的语法结构。
由输出项，列表项，过滤项组成，过滤项为bool值可省略
[expr for itm in collection if condition] 列表常规推导

lst = [11,22,33,44]
result = [i for i in range(10) if i%2==0]
print(result)

#注意是==,否则报错

lst = [11,22,33,44]
result = [i for i in lst if i%2==0]
print(result)

zero = [0,-1,5,3,-9,-3,6,2]
zero_list = [x**2 for x in zero if x >0]
print(zero_list)

 

(expr for itm in collection if condition) 列表迭代推导,

也可以说是生成器表达式,这个给出的结果是一个生成器

lst = [11,22,33,44]
result = (i for i in lst if i%2==0)
print(result)

<generator object <genexpr> at 0x0000000004DA9F68>

{key: value for (key, value) in iterable}字典推导

lst=[1,2,3,4,5]
res={i:'python'+str(i)+'期' for i in lst if i>3}
print(res)

打印结果:{4: 'python4期', 5: 'python5期'}

{expr for itm in collection if condition} 集合推导

 

lst=[1,2,3,4,5,5,2,3]
res={i for i in lst if i>0}
print(res)

# 结果直接过滤重复元素

{1, 2, 3, 4, 5}