由于Python的if语句与C语言非常类似，同时python作为高级语言和我们平时使用英文非常接近，所以直接用例子来描述if语句的语法：
ages = (20, 21) if ages[1] > 18 and ages[0] > 18: print('They are all adults') if 18 in ages: print('18 is in ages') else: print('18 is not in ages') requested_toppings = ['mushroom', 'extra cheese', 'green peppers'] if 'mushroom' in requested_toppings: print('Adding mushroom') if 'extrea cheese' in requested_toppings: print('Adding mushroom') if 'green peppers' not in requested_toppings: print('OK') else: print('green peppers is out of sales') print('Finish!') requested_toppings = [] if requested_toppings: for requested_topping in requested_toppings: print('Adding' + requested_topping) else: print('making plaint pizza')if语句的一些格式
if 语句1 or 语句2 if语句1 and 语句2 if 元素 in 列表 if 元素 not in 列表