number_list = [1,2,3,4,5,6]
for i in number_list:
if i==1:
print(i)
else:
print("?")
5.2 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，这种表达式称 为条件测试。Python根据条件测试的值为True还是False来决定是否执 行if语句中的代码。如果条件测试的值为True，Python就执行紧跟 在if语句后面的代码；如果为False，Python就忽略这些代码。
5.2.1 检查是否相等number_list = [1,2,3,4,5,6]
for i in number_list:
if i==1:
print(i)
5.2.2 检查不相等
number_list = [1,2,3,4,5,6]
for i in number_list:
if i!=1:
print(i)
5.2.3 数字比较
# > < >= <=5.2.4 检查多个条件
- and
- or
number_list = ['a','b','c']
number = "a"
# 包含
if number in number_list:
print(number)
# 不包含
if number not in number_list:
print(number_list[1],number_list[2])
5.2.6 布尔表达式
car = 'subaru'
print("Is car == 'subaru'? ")
print(car == 'subaru')
print("nIs car == 'audi'? ")
print(car == 'audi')
5.3 if语句
5.3.1 简单的if
age = 19
if age > 18:
print("比它大")
5.3.2 if-else
age = 19
if age > 18:
print("比它大")
else:
print("比它小")
5.3.3 if-elif-else
- 支持使用多个elif
- 可省略else
age = int(12)
if age < 4:
print("大了")
elif age < 12:
print("还是大了")
else:
print("对了")
5.4 if处理列表
5.4.1 检查列表元素
list = ["aa","bb","cc"]
for i in list:
if i == "aa":
print("aa")
else:
print(i)
5.4.2 确定列表不是空的
requested_toppings = []
if requested_toppings:
for requested_topping in requested_toppings:
print(f"Adding {requested_topping}.")
print("nFinished making your pizza!")
else:
print("Are you sure you want a plain pizza?")
