控制流

if / elif / else

score = 85
if score >= 90:
    level = "A"
elif score >= 80:
    level = "B"
else:
    level = "C"

for i in range(3):
    print(i)  # 0 1 2

for ch in "hi":
    print(ch)

for k, v in {"a": 1, "b": 2}.items():
    print(k, v)

n = 3
while n > 0:
    print(n)
    n -= 1

for i in range(5):
    if i == 2:
        continue  # 跳过本轮
    if i == 4:
        break     # 结束循环
    print(i)
# 输出：0 1 3

squares = [x * x for x in range(5)]       # [0,1,4,9,16]
evens = [x for x in range(10) if x % 2 == 0]
mapping = {x: x * x for x in range(3)}

可读性优先：推导式适合「简单映射/过滤」，复杂逻辑仍用普通循环。