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CSDN 课程推荐《8小时Python零基础轻松入门》讲师齐伟苏州研途教育科技有限公司CTO苏州大学应用统计专业硕士生指导委员会委员已出版《跟老齐学Python轻松入门》《跟老齐学PythonDjango实战》、《跟老齐学Python数据分析》和《Python大学实用教程》畅销图书。Python3 基础学习笔记第四章【if 语句】目录【4.1】一个简单的数列 【4.1.1】检查特定值是否包含在列表当中 【4.2】if-else 语句 【4.3】if-elif-else 结构 【4.3.1】使用多个 elif 代码块 【4.3.2】省略 else 代码块 【4.4】测试多个条件 【4.5】使用 if 语句处理列表 【4.5.1】检查特殊元素【4.5.2】确定列表不是空的【4.5.3】使用多个列表【4.1】一个简单的数列
给定一个汽车列表将其中每一辆汽车的名称打印出来要求打印 ‘bmw’ 时所有字母都要大写其余名称只需要首字母大写 cars [audi , bmw , subaru , toyota]for car in cars:if car bmw:print(car.upper())else:print(car.title())输出结果如下
Audi
BMW
Subaru
Toyota【4.1.1】检查特定值是否包含在列表当中 要判断特定的值是否已包含在列表当中可使用关键字 in user_names [andia , david , liwa]user andiaif user in user_names:print(user.title() is in user_name.)输出结果如下
Andiais in user_name.要判断特定的值是否不包含在列表当中可使用关键字 not in user_names [andia , david , liwa]user kivleif user not in user_names:print(user.title() is not in user_name.)输出结果如下
Kivleis not in user_name.【4.2】if-else 语句 age input(请输入你的年龄查看是否可以去网吧)if int(age) 18:print(You are old enough to go to the net bar!)print(You should go to net bar less,study more!)else:print(You are too young to go to the net bar!)print(Wait until you are 18 to go to the net bar!)分别输入19和15输出结果如下 请输入你的年龄查看是否可以去网吧19You are old enough to go to the net bar!You should go to net bar less,study more!请输入你的年龄查看是否可以去网吧15You are too young to go to the net bar!Wait until you are 18 to go to the net bar!【4.3】if-elif-else 结构 age 12if age 4:price 0elif age 18:price 5else:price 10print(Your admission cost is $ str(price) .)输出结果如下 Your admission cost is $5.【4.3.1】使用多个 elif 代码块
age 20
if age 4:price 0
elif age 18:price 5
elif age 65:price 15
else:price 10
print(Your admission cost is $ str(price) .)输出结果如下
Your admission cost is $15.【4.3.2】省略 else 代码块
Python并不要求 if-elif 结构后面必须有 else 代码块
age 20
if age 4:price 0
elif age 18:price 5
elif age 65:price 15
elif age 65:price 10
print(Your admission cost is $ str(price) .)输出结果仍与3.3.1一样
【4.4】测试多个条件
if-elif-else结构功能强大但仅适用于只有一个条件满足的情况遇到通过了的测试后Python就会跳过余下的测试 names [Zhangshan , Wanger]
if Zhangshan in names:print(Zhangshan is here!)
if Wanger in names:print(Wanger is here!)
if Xiaoming in names:print(Xiaoming is here!)
print(All the students are here!)输出结果如下
Zhangshan is here!
Wanger is here!
All the students are here!相同的程序如果使用 if-elif-else 结构代码将不能正确运行
names [Zhangshan , Wanger]
if Zhangshan in names:print(Zhangshan is here!)
elif Wanger in names:print(Wanger is here!)
elif Xiaoming in names:print(Xiaoming is here!)
print(All the students are here!)输出结果如下
Zhangshan is here!
All the students are here!总之如果我们只想执行一个代码块就使用 if-elif-else 结构如果要运行多个代码块就必须使用一系列独立的 if 语句
【4.5】使用 if 语句处理列表
【4.5.1】检查特殊元素
对3.4例子改版加入姓名 ‘Xiaoming’当检索到Xiaoming时告诉他他妈妈叫他回家吃饭
names [Zhangshan , Wanger , Xiaoming]
for name in names:if name Xiaoming:print(Xiaoming,Your mother told you to go home for dinner!)else:print(name is here!)
print(All the students are here!)输出结果如下
Zhangshanis here!
Wangeris here!
Xiaoming,Your mother told you to go home for dinner!
All the students are here!【4.5.2】确定列表不是空的
在检索姓名前检查姓名是否为空不为空则打印出所有姓名为空则提示没有姓名
names []
if names:for name in names:print(name is here!)print(All the students are here!)
else:print(There is no students!)输出结果如下
There is no students!在if语句中将列表名用在条件表达式中时Python将在列表至少包含一个元素时返回Ture并在列表为空时返回False
【4.5.3】使用多个列表
两个列表names_1和names_2要求输出既在names_2中又在names_1中的元素
names_1 [Zhangshan , Liyang , Wanger , Tangyang , Xiaoming]
names_2 [Liyang , Zhangwei , Tangyang]
for names in names_2:if names in names_1:print(names is here!)
print(All the students are here!)输出结果如下
Liyang is here!
Tangyang is here!
All the students are here!
