帶有判斷條件的表達(dá)式為
[Expression for target in iterable if condition]
列表推導(dǎo)式的執(zhí)行順序.png
列表推導(dǎo)式實(shí)現(xiàn)嵌套的表達(dá)式為
[Expression for target1 in iterable 1
for target2 in iterable 2
......
for targetn in iterable n
使用推導(dǎo)式將二維列表降維：
matrix = [[1,2,3],
[4,5,6],
[7,8,9]]
[j for i in matrix for j in i]
# 打印結(jié)果為
[1, 2, 3, 4, 5, 6, 7, 8, 9]
用嵌套循環(huán)的方式寫(xiě)
matrix = [[1,2,3],
[4,5,6],
[7,8,9]]
a = []
for i in matrix:
for j in i:
a.append(j)
print(a)
# 輸出結(jié)果為
[1, 2, 3, 4, 5, 6, 7, 8, 9] #嵌套循環(huán)幫助理解推導(dǎo)式的內(nèi)容
列表推導(dǎo)式的終極表達(dá)式
[Expression for target1 in iterable 1 if condition
for target2 in iterable 2 if condition
......
for targetn in iterable n if condition
舉例
for x in range(10):
if x % 2 == 0:
for y in range(10):
if y % 3 == 0:
print([x,y])
# 等同于下面的列表推導(dǎo)式寫(xiě)法
[[x,y] for x in range(10) if x % 2==0 for y in range(10) if y % 3 ==0]
[[0, 0], [0, 3], [0, 6], [0, 9], [2, 0], [2, 3], [2, 6], [2, 9], [4, 0], [4, 3], [4, 6], [4, 9], [6, 0], [6, 3], [6, 6], [6, 9], [8, 0], [8, 3], [8, 6], [8, 9]]
