列表推導式和字典推導式是什么？

它們是可以輕松創建字典和列表的語法結構。
由輸出項，列表項，過濾項組成，過濾項為bool值可省略
[expr for itm in collection if condition] 列表常規推導

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

#注意是==,否則報錯

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) 列表迭代推導,

也可以說是生成器表達式,這個給出的結果是一個生成器

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}字典推導

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

打印結果:{4: 'python4期', 5: 'python5期'}

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

 

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

# 結果直接過濾重復元素

{1, 2, 3, 4, 5}