Loading... # 第四章 if语句 ## 4.1 条件测试 ### 4.1.1 检查是否相等 ```python car = 'bmw' print(car == 'bmw') print(car == 'byd') print(car != 'byd') ``` 输出结果: > True > False > True - `==` 等于 - `!=` 不等于 - `>, >=, <, <=` 大小于等于 ### 4.1.2 检查多个条件 ```python car = 'bmw' phone = 'iphone' print(car == 'bmw' and phone == 'iphone') print(car == 'byd' or phone == 'samsung') ``` > True > False - `and` 逻辑且 - `or` 逻辑或 ### 4.1.3 检查特定值是否在列表中 ```python nums = [10, 20, 30] print(30 in nums) print(40 not in nums) ``` > True > True - `in` 在列表中 - `not in`不在列表中 ### 4.1.4 布尔表达式 ```python flag = True flag = False ``` 不多赘述 ## 4.2 if语句 ```python age = 15 if age >= 18: print("You are old enough") print("You can vote now") ``` !!! Python的if语句不需要加括号。<b><u>注意冒号</b></u> !!! ### 4.2.1 if-else语句 ```python age = 15 if age >= 18: print("You are old enough") print("You can vote now") else: print("You are too young") print("Please wait for " + str(18-age) + " year(s)") ``` 输出结果: > You are too young > Please wait for 3 year(s) ### 4.2.2 if-elif-else语句 ```python age = 15 if age >= 18: print("You are an adult") elif age >= 12: print("You are a teenager") else: print("You are a child") ``` 输出结果: > You are a teenager ### 4.2.3 检查列表是否为空 ```python nums = [] if nums: print("list is not empty") else: print("list is empty") ``` 输出为: > list is empty ### 4.2.4 if语句与布尔表达式 ```python flag = True if flag: print("YES") else: print("NO") ``` 输出: > YES 不多赘述 最后修改:2021 年 08 月 01 日 03 : 00 PM © 允许规范转载