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2019/7/12 python入门-if

Posted on By LuLu

python入门-if

if

if-elif-else

age=12
if age<4:
	price=4
elif age<18:
	price=5
else :
	price=6
print("cost is "+str(price)+".")
  • 简单例子,注意写法elif,用price的值更便于修改
requested_toppings=['mushrooms','extra cheese']
if 'mushrooms' in requested_toppings:
	print("Hold the anchovies")
if 'extra cheese' in requested_toppings:
	print("add the anchovies")
  • 当要测试多个条件时,应该使用不包括elif和else的if语句,可能多个条件为true
  • 如果使用了elif和else,当满足一个条件时就会退出,不会继续判断剩余条件

使用if语句处理列表

requested_toppings=['mushrooms','green peppers','extra cheese']
for requested_topping in requested_toppings :
	if requested_topping =='green peppers':
		print("we dont have peppers")
	else:
		print("Adding "+requested_topping+' .')
print("\n finish this pizza")
  • 对for中某个元素进行单独操作时可以用到if
requested_toppings1=[]
if requested_toppings1:
	for requested_topping in requested_toppings :
		print("Adding "+requested_topping+' .')
else:
	print("Are you sure?")
  • 确定列表元素不为空,即列表名在条件表达式中,至少含有一个元素为true,列表为空返回False,在进行for循环之前,对列表是否为空进行检查十分必要
requested_toppings=['mushrooms','french fries','extra cheese']
available_toppings=['mushrooms','green peppers','extra cheese']
for requested_topping in requested_toppings :
	if requested_topping in available_toppings:
		print("Adding "+requested_topping+' .')
	else:
		print("we dont have "+requested_topping)
print("\n finish this pizza")
  • if语句使用多个列表

if语句的格式

if age > 4:
  • 在><或者≥,≤运算符左右两边都嫁一个空格