Python学习-if语句

又要到周末，要放假了，上午专业案例课，老师全在讲arcgis的操作，跟遥感有关的，第四节操作课了，我一节课没听，先暂时不理会这个软件，以后方向研究上跟遥感牵扯的点很少。下午的遥感课，老师一个人在上面讲得得劲儿，下面的学生零星几个在听课，实惨！

今天主要学了if语句相关的知识，如何编写简单的if语句、if-else语句、if-elif-else语句、检查元素是否在列表里、使用多个列表等。这几天学的知识没来得及复习，真正开始学习起来才知道，时间是真的很不够用，需要学习的课程太多，很难一并抓起来，之前立了个flag，在12月前要把这本Python入门的书学完并且掌握好它，为之后的学习打下基础。

#10.29练习
cars=["bmw","audi","toyota","subaru"]
for car in cars:if car=="bmw":     #此处也需要冒号（：） #检查当前汽车名是否为bmw,如果是，则全以大写方式打印print(car.upper())else:print(car.title())car="bmw"
print(car=="b")   #一个等号是陈述，两个等号是发问，两个等号可以解读为变量“car”的值是“bmw”吗words="xiaohao love the girl"
if words!="xiaohao":  #!= 不等于print(words)age=18
print(age==18)answer=18
if answer!=19:print("hahahha")age_0=18
age_1=20
print(age_0>=17 and age_1<=25)   #用and检查多个文件
print((age_0>=17)and(age_1<=25))   #也可以用and连接分开表达
print(age_0>=17 or age_1<=25)     ##用or检查多个文件cars=["bmw","audi","toyota","subaru"]
print("bmw"in cars)      #用in来检查特定值是否包含在列表中
print("audi"in cars)
print("xiaoma"in cars)
print(19 in cars)cars=["bmw","audi","toyota","subaru"]
if "bmw" not in cars:     #此处“bmw”可以用一个变量来定义，如xiaoma="bmw"print("xiaoma")
else:print(f'this my hometown {cars[3].upper()}!')
#P69小练习
car="toyota"
print("Is car=='toyota'? I predict True.")
print(car=="bmw")
print("\nIs car=='audi'?I predict False.")
print(car=="bmw")
xiaoli="boy"
print(xiaoli=="boy")
print(xiaoli=="girl")
xiaohao="good boy"
if xiaohao!="bad boy":print(xiaohao)age_0=20
age_1=21
age_2=22
print(age_0==18)
print(age_1==21)
print(age_0>=15 and age_1<=30)
print((age_2>=20)and (age_1>=16))
if age_2!=23:print(age_0)
cars=["bmw","audi","toyota","subaru"]
if "hah"in cars:print(f"My hometown very good!the {cars[3].upper()} is good!")
else:print("xiaohao zui niubi")
cars=["bmw","audi","toyota","subaru"]
if "hah" not in cars:print(f"My hometown very good!the {cars[3].upper()} is good!")
else:print("xiaohao zui niubi")
if conditional_test:do something
age=19
if age>=15:print("You are welcome!")
age=20
if age>=16:print("mymymymymy")   #if语句中的缩进跟for循环的缩进相同print("hahahahahhah")
#if-else语句
age=20
if age>=23:print("good!")print("You are my person!")
else:print("worry!")print("Go back!")
#if-elif-else语句
age=18
if age<10:print("go")
elif age<=18:     #elif代码仅在前面测试未通过的情况下才会运行print("come")
else:print("go out!")
xiaohao=["xiaojin","xiaobing","xiaopei"]
if "xiaoji"in xiaohao:print("go")
elif "xiaobing" in xiaohao:print("come")
else:print("go out!")
age=25
if age<12:price=0
elif age<=18:    #s使用多个elif测试块，跟使用单个elif测试块原理相同price=50
elif age <= 30:price = 80
else:price=100
print(f"you admission cost is ${price}!")   #输入句子向用户指明门票价格age=25
if age<12:price=0
elif age<=18:price=50
elif age <= 30:   #Python中可以省略else代码块price = 80
print("hahahha")
age=25
if age<12:price=0
if 12<=age<=30:  #多个elif代码块可用多个if语句代替price=50
print(f"the ${price}!")
#P75小练习
alien_color="green"
if alien_color=="green":print("你获得了5积分！")    #if语句中变量只能用“!=”“==”等连接，不能直接用单等号“=”
else:print("我错了")
alien_color="yellow"
if alien_color=="green":print("你获得了5积分！")alien_color="yellow"
if alien_color=="green":print("你因射杀该外星人获得5积分")
else:print("你获得了10积分")alien_color="yellow"
if alien_color=="green":print("你获得了5分")
elif alien_color=="yellow":print("你获得了10积分")
else:print("你获得了15积分")age=1000
if age<2:print("我还是个婴儿")
elif age>=2 and age<4:print("我是个幼儿")
elif age>=4 and age<13:print("我是个儿童")
elif age>=13 and age<20:print("我是个青少年")
elif age>=20 and age<65:print("我是个成人啦")
else:print("我是一个老年人啦，不要欺负我哦！")
favorite_fruits=["apple","orange","banana"]
fruit="hahah"
if fruit in favorite_fruits:   #可以定义一个变量，用变量加到for循环中print("You really like apple!")
else:print("oh no")
favorite_fruits=["apple","orange","banana"]
if "apple" in favorite_fruits:   #可以直接不定义变量直接加到for循环语句中print("You really like apple!")
I_want_eat=["noddle","rice","apple"]
for apples in I_want_eat:print(apples)
print("I want to eat!")
I_want_eat=["noddle","rice","apple"]
for apples in I_want_eat:if apples=="haha":print("hahhahahahahah")else:print("xiaohaihai")
print("\n我要吃这个")
#确定列表是不是空的
favorite_fruits=[]    #创建一个空列表用于检验
if favorite_fruits:for favorite_fruit in favorite_fruits:print(f"Adding {favorite_fruit}.")print("\nFinished making your pizza!")
else:print("Are you sure you want a plain pizza?")
available_topping=["mushrooms","olives","green peppers","pepperoni"]   #披萨店供应的配料
requested_toppings=["mushrooms","french fries","extra cheese"]   #顾客点的配料
for requested_topping in requested_toppings:   #遍历顾客点的配料if requested_topping in available_topping:  #检查顾客点的配料是否在店铺供应的配料中print(f"Adding {requested_topping}.")else:print(f"Sorry,we don't have {requested_topping}.")
print("\nFinished making your pizza!")
#P78小练习
users=["admin","xiaolei","xiaoyang","xiaoli"]
for user in users:if user=="admin":print(f"Hello {user},woeld you like to see a status report?")else:print(f"Hello {user},thank you for logging in again")
users=["admin","xiaolei","xiaoyang","xiaoli"]
del users[0:4]
print(users)
users=[]
if users:for user in users:print(user)else:print("We need to find some users!")
names=[]
if names:for name in names:if name=='admin':print('\nHello Admin,would you like to see a status report?')else:print('\nHello '+name.title()+',thank you for logging in again.')
else:print('We need to find some users.')
current_users=["xiaolei","xiaoyang","xiaocao","xiaofang","xiaogan"]
new_users=["xiaoha","xiaowang","xiaolei","xiaoyang","xiaodi"]
for new_user in new_users:if new_user in current_users:print("我需要别的用户")else:print(f"{new_user}未被使用")
current_users=["xiaolei","xiaoyang","xiaocao","xiaofang","xiaogan"]
current_users_1=["xiaolei","xiaoyang","xiaocao","xiaofang","xiaogan"]
new_users=["xiaoha","xiaowang","xiaolei","xiaoyang","xiaodi"]
for new_user in new_users:if new_user in current_users:print("我需要别的用户")else:print(f"{new_user}未被使用")
numbers=list(range(1,10))
print(numbers)
for number in numbers:if number == 1:print(str(number)+"st")elif number==2:print(str(number)+"nd")elif number==3:print(str(number)+"rd")else:print(str(number)+"th")#if语句格式设置，在诸如== >= <=等比较运算符两边各添加一个空格

明天周六，虽然放假，但还是得继续学习，明天继续来教室。

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