1. 条件测试 每条if 语句的核心都是一个值为True 或False 的表达式，这种表达式被称为条件测试 。
==, !=, <, <=, >, >= and, or 检查特定值是否包含在列表中, in / not inbanned_users = ['andrew', 'carolina', 'david']user = 'marie'if user not in banned_users: PRint(user.title() + ", you can post a response if you wish.")2. if 语句 (1).简单的if 语句
age = 19if age >= 18: print("You are old enough to vote!")(2).if-else 语句
age = 17if age >= 18: print("You are old enough to vote!") print("Have you registered to vote yet?")else: print("Sorry, you are too young to vote.") print("Please register to vote as soon as you turn 18!")(3).if-elif-else 结构
age = 12if age < 4: print("Your admission cost is $0.")elif age < 18: print("Your admission cost is $5.")else: print("Your admission cost is $10.")(4).使用多个elif 代码块
age = 12if age < 4: price = 0elif age < 18: price = 5elif age < 65: price = 10else: price = 5print("Your admission cost is $" + str(price) + ".")(5).省略else 代码块 Python并不要求if-elif 结构后面必须有else 代码块。
3. 使用if 语句处理列表 确定列表不是空的 在if 语句中将列表名用在条件表达式中时，Python将在列表至少包含一个元素时返回True ，并在列表为空时返回False 。
requested_toppings = []if requested_toppings: for requested_topping in requested_toppings: print("Adding " + requested_topping + ".") print("/nFinished making your pizza!")else: print("Are you sure you want a plain pizza?")新闻热点
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