age = 18
if age >= 18:
    print("你已成年，可以投票！")

print(5 > 3)        # True
print("a" == "A")   # False（區(qū)分大小寫）
print(10 != 20)     # True

if []: 
    print("不會(huì)執(zhí)行")
if "Hello":
    print("非空字符串為 True")  # 會(huì)執(zhí)行

score = 85
if score >= 60:
    print("及格！")
else:
    print("不及格，請(qǐng)努力！")

a = int(input("請(qǐng)輸入您的年齡："))
if a < 10:
    print("您是兒童")
elif a < 16:
    print("您是少年")
else:
    print("您比少年大")

a = int(input("請(qǐng)輸入您的年齡："))
if a < 10:
    print("您是兒童")
elif a < 16:
    print("您是少年")
elif a < 30:
    print("您是青年")
elif a < 59:
    print("您是中年人")
else:
    print("您是老年人")

a = int(input("請(qǐng)輸入您的年齡："))
if a < 10:
    if a < 1:        
        print("您是嬰兒")
    else:
        print("您是兒童")
elif a < 16:
    print("您是少年")
else:
    print("您比少年大")

username = "admin"
password = "123456"

if username == "admin" and password == "123456":
    print("登錄成功！")
else:
    print("用戶名或密碼錯(cuò)誤")

表達(dá)式1 if 條件判斷語句 else 表達(dá)式2

age = 20
status = "成年" if age >= 18 else "未成年"
print(status)  # 成年

# 也可用于 print
print("及格" if score >= 60 else "不及格")

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

for i in range(5):
    print(f"第 {i+1} 次循環(huán)")

# 普通寫法
squares = []
for x in range(5):
    squares.append(x ** 2)

# 列表推導(dǎo)式（推薦）
squares = [x ** 2 for x in range(5)]
print(squares)  # [0, 1, 4, 9, 16]

count = 0
while count < 3:
    print(f"計(jì)數(shù)：{count}")
    count += 1  # 必須有退出機(jī)制，否則死循環(huán)！

import time

for i in range(60):  
    for j in range(60):  
        time.sleep(1)  
        print(f'當(dāng)前時(shí)間為 {i} 分 {j} 秒')
    print(f"{i} 分鐘結(jié)束")

# break：找到目標(biāo)就停止
for num in [1, 3, 5, 7, 9]:
    if num == 5:
        print("找到 5，退出循環(huán)")
        break
    print(num)

# continue：跳過偶數(shù)
for i in range(1, 6):
    if i % 2 == 0:
        continue
    print(i)  # 輸出：1, 3, 5

try:
    n = int(input("請(qǐng)輸入一個(gè)整數(shù)："))
    print(n)
except:
    print("您輸入的不是一個(gè)整數(shù)")
a = 3
print("a的內(nèi)容為：", a)

try:
    # 可能出錯(cuò)的代碼
except ExceptionType1:
    # 處理異常1
except ExceptionType2:
    # 處理異常2
else:
    # 無異常時(shí)執(zhí)行
finally:
    # 無論是否有異常，都會(huì)執(zhí)行（常用于清理資源）

try:
    num = int(input("請(qǐng)輸入一個(gè)數(shù)字："))
    result = 100 / num
except ValueError:
    print("輸入的不是有效數(shù)字！")
except ZeroDivisionError:
    print("不能除以零！")
except Exception as e:
    print(f"發(fā)生了未知錯(cuò)誤：{e}")
else:
    print(f"結(jié)果是：{result}")
finally:
    print("程序結(jié)束。")

while True:
    try:
        weight = float(input('請(qǐng)輸入白菜的重量：'))
        break
    except:
        print("輸入錯(cuò)誤，重新輸入，", end='')
if weight < 2.0:
    print("請(qǐng)付款：", weight*2.5*0.9, '元')
elif weight < 4.0:
    print("請(qǐng)付款：", weight*2.5*0.8, '元')
elif weight < 10.0:
    print("請(qǐng)付款：", weight*2.5*0.6, '元')
else:
    print("請(qǐng)付款：", weight*2.5*0.4, '元')

while True:
    try:
        weight = float(input('請(qǐng)輸入白菜的重量：'))
        if weight < 2.0:
            print("請(qǐng)付款：", weight*2.5*0.9, '元')
        elif weight < 4.0:
            print("請(qǐng)付款：", weight*2.5*0.8, '元')
        elif weight < 10.0:
            print("請(qǐng)付款：", weight*2.5*0.6, '元')2
        else:
            print("請(qǐng)付款：", weight*2.5*0.4, '元')
    except:
        print("輸入錯(cuò)誤，重新輸入，", end='')