python基础三之（三元表达式、（列表，字典）生成式、生成器表达式）

普通实现：

# def max2(x,y):
# if x > y:
# return x
# else:
# return y
# res=max2(1,3)

三元表达式实现：

x=10
y=30
 
res=x if x > y else y
print(res)
 

　　

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列表生成式

普通实现：

l=[]
for i in range(10):
l.append('egg%s' %i)
 
print(l)

式列表生成式实现

l=['egg%s' %i for i in range(10)]
print(l)
 
nums=[i**2 for i in range(10)]
print(nums)
 
 
nums=[i for i in range(10) if i > 3]
print(nums)

例题：

1、将names=['egon','alex_sb','wupeiqi','yuanhao']中的名字全部变大写

names=['egon','alex_sb','wupeiqi','yuanhao']
names=[name.upper() for name in names]
print(names)
 

2、将names=['egon','alex_sb','wupeiqi','yuanhao']中以sb结尾的名字过滤掉，然后保存剩下的名字长度

names=['egon','alex_sb','wupeiqi','yuanhao']
l=[len(name) for name in names if not name.endswith('sb')]
print(l)
 

字典生成式

d={i:i for i in range(10) if i > 0}
print(d)
userinfo=[('egon','123'),('alex','456'),('wxx','679')]
dic={k:v for k,v in userinfo}
print(dic)
 

 

生成器表达式

g=(i for i in range(100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000))
# print(g)
print(next(g))
print(next(g))
print(next(g))
print(next(g))
print(next(g))
print(next(g))
print(next(g))
 
chicken=('egg%s' %i for i in range(3))
# print(chicken)
print(next(chicken))
print(next(chicken))
print(next(chicken))
print(next(chicken))

　

求文件a.txt中最长的行的长度（长度按字符个数算，需要使用max函数）

res=max((1,2,3,4,5,6,7))
print(res)
 
with open('a.txt','r',encoding='utf-8') as f:
nums=(len(line) for line in f)
# print(nums)
# print(nums)
# print(next(nums))
 
print(max(nums))