条件判断进阶

1. 多分支与条件组合

score = 86
if score >= 90:
   level = "A"
elif 80 <= score < 90:
   level = "B"
elif 70 <= score < 80:
   level = "C"
else:
   level = "D"
print(level)

1. 三元表达式

a, b = 3, 5
max_value = a if a > b else b

循环控制与 else 子句

1. for/while + else

nums = [2, 4, 6, 9, 10]
for n in nums:
   if n % 2 == 1:
       print("发现奇数", n)
       break
else:
   print("未发现奇数")

1. continue/ break 的常见误区

for i in range(5):
   if i == 2:
       continue  # 跳过2，但循环继续
   if i == 4:
       break     # 提前结束循环
   print(i)

列表/字典推导式与条件过滤

squares_of_even = [x*x for x in range(10) if x % 2 == 0]
index_map = {c: i for i, c in enumerate("abcde", start=1)}

小练习：质数判定

def is_prime(n: int) -> bool:
   if n < 2:
       return False
   for d in range(2, int(n ** 0.5) + 1):
       if n % d == 0:
           return False
   return True

print([x for x in range(2, 30) if is_prime(x)])

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