本文记录是自己这个小菜鸡Python学习笔记
《Python编程从入门到实践》第五章
#第5章 if语句
#5.1 一个简单示例
cars = ['audi', 'bmw', 'subaru', 'toyota']
for car in cars:
if car == 'bmw':
print(car.upper())
else:
print(car.title())
'''
Audi
BMW
Subaru
Toyota
'''
#5.2 条件测试
#检查是否相等
'''
>>> car = 'bmw'
>>> car == 'bmw'
True
'''
'''
>>> car = 'audi'
>>> car == 'bmw'
False
'''
#检查是否相等时不考虑大小写
'''
>>> car = 'Audi'
>>> car == 'audi'
False
'''
'''
>>> car = 'Audi'
>>> car.lower() == 'audi'
True
'''
'''
>>> car = 'Audi'
>>> car.lower() == 'audi'
True
>>> car
'Audi'
'''
#检查是否不相等
requested_topping = 'mushrooms'
if requested_topping != 'anchovies':
print("Hold the anchovies!")
'''
Hold the anchovies!
'''
#比较数字
'''
>>> age = 18
>>> age == 18
True
'''
answer = 17
if answer != 42:
print("That is not the correct answer. Please try again!")
'''
That is not the correct answer. Please try again!
'''
'''
>>> age = 19
>>> age < 21
True
>>> age <= 21
True
>>> age > 21
False
>>> age >= 21
False
'''
#检查多个条件
#使用and检查多个条件
#and 相当于 与
'''
>>> age_0 = 22
>>> age_1 = 18
>>> age_0 >= 21 and age_1 >= 21
False
>>> age_1 = 22
>>> age_0 >= 21 and age_1 >= 21
True
(age_0 >= 21) and (age_1 >= 21)
'''
#使用or检查多个条件
#or 相当于 或
'''
>>> age_0 = 22
>>> age_1 = 18
>>> age_0 >= 21 or age_1 >= 21
True
>>> age_0 = 18
>>> age_0 >= 21 or age_1 >= 21
False
'''
#检查特定值是否包含在列表中
'''
>>> requested_toppings = ['mushrooms', 'onions', 'pineapple']
>>> 'mushrooms' in requested_toppings
True
>>> 'pepperoni' in requested_toppings
False
'''
#检查特定值是否不包含在列表中
banned_users = ['andrew', 'carolina', 'david']
user = 'marie'
if user not in banned_users:
print(user.title() + ", you can post a response if you wish.")
'''
Marie, you can post a response if you wish.
'''
#布尔表达式
game_active = True
can_edit = False
#5.3 if语句
#简单的if语句
'''
if conditional_test:
do something
'''
age = 19
if age >= 18:
print("You are old enough to vote!")
'''
You are old enough to vote!
'''
age = 19
if age >= 18:
print("You are old enough to vote!")
print("Have you registered to vote yet?")
'''
You are old enough to vote!
Have you registered to vote yet?
'''
#if-else语句
age = 17
if 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!")
'''
Sorry, you are too young to vote.
Please register to vote as soon as you turn 18!
'''
#if-elif-else 结构
age = 12
if age < 4:
print("Your admission cost is $0.")
elif age < 18:
print("Your admission cost is $5.")
else:
print("Your admission cost is $10.")
'''
Your admission cost is $5.
'''
age = 12
if age < 4:
price = 0
elif age < 18:
price = 5
else:
price = 10
print("Your admission cost is $" + str(price) + ".")
'''
Your admission cost is $5.
'''
#使用多个 elif 代码块
age = 12
if age < 4:
price = 0
elif age < 18:
price = 5
elif age < 65:
price = 10
else:
price = 5
print("Your admission cost is $" + str(price) + ".")
'''
Your admission cost is $5.
'''
#省略 else 代码块
age = 12
if age < 4:
price = 0
elif age < 18:
price = 5
elif age < 65:
price = 10
elif age >= 65:
price = 5
print("Your admission cost is $" + str(price) + ".")
'''
Your admission cost is $5.
'''
#测试多个条件
requested_toppings = ['mushrooms', 'extra cheese']
if 'mushrooms' in requested_toppings:
print("Adding mushrooms.")
if 'pepperoni' in requested_toppings:
print("Adding pepperoni.")
if 'extra cheese' in requested_toppings:
print("Adding extra cheese.")
print("nFinished making your pizza!")
'''
Adding mushrooms.
Adding extra cheese.
Finished making your pizza!
'''
requested_toppings = ['mushrooms', 'extra cheese']
if 'mushrooms' in requested_toppings:
print("Adding mushrooms.")
elif 'pepperoni' in requested_toppings:
print("Adding pepperoni.")
elif 'extra cheese' in requested_toppings:
print("Adding extra cheese.")
print("nFinished making your pizza!")
'''
Adding mushrooms.
Finished making your pizza!
'''
#5.4 使用 if 语句处理列表
#检查特殊元素
requested_toppings = ['mushrooms', 'green peppers', 'extra cheese']
for requested_topping in requested_toppings:
print("Adding " + requested_topping + ".")
print("nFinished making your pizza!")
'''
Adding mushrooms.
Adding green peppers.
Adding extra cheese.
Finished making your pizza!
'''
requested_toppings = ['mushrooms', 'green peppers', 'extra cheese']
for requested_topping in requested_toppings:
if requested_topping == 'green peppers':
print("Sorry, we are out of green peppers right now.")
else:
print("Adding " + requested_topping + ".")
print("nFinished making your pizza!")
'''
Adding mushrooms.
Sorry, we are out of green peppers right now.
Adding extra cheese.
Finished making your pizza!
'''
#确定列表不是空的
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?")
'''
Are you sure you want a plain pizza?
'''
#使用多个列表
available_toppings = ['mushrooms', 'olives', 'green peppers',
'pepperoni', 'pineapple', 'extra cheese']
requested_toppings = ['mushrooms', 'french fries', 'extra cheese']
for requested_topping in requested_toppings:
if requested_topping in available_toppings:
print("Adding " + requested_topping + ".")
else:
print("Sorry, we don't have " + requested_topping + ".")
print("nFinished making your pizza!")
'''
Adding mushrooms.
Sorry, we don't have french fries.
Adding extra cheese.
Finished making your pizza!
'''
#5.5 设置 if 语句的格式
'''
在诸如==、>=和<=等比较运算符两边各添加一个空格
例如，if age < 4:要比if age<4:好
'''
