python之三元表达式、列表推导、生成器表达式、递归、匿名函数、内置函数

一、三元表达式

def max(x,y):
    return x if x>y else y
print(max(10,12))

name=input('>>>')
res='sb' if name=='alex' else 'nb'
print(res)
'''
name=input('>>>')
res='sb'
if name=='alex':
    print(res')
else:
    print('nb')
'''

二、列表推导

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

egg_list=['鸡蛋%s'%i for i in range(10)]
print(egg_list)

'''
优点是方便、改变了编程习惯，可被称为声明式编程
'''

三、生成器表达式

'''
把列表推导中的[]换成()生成器表达式
其优点是节省内存，一次在内存中只产生一个值
'''
bamboo=('竹节%s节'%i for i in range(1,11))
print(bamboo)#生成器表达式内存地址
print(next(bamboo))
print(list(bamboo))

names=['cindy','sara','chengjie','mark']
li=(i.capitalize() for i in names)
print(list(li))#['Cindy', 'Sara', 'Chengjie', 'Mark']

with open('a.txt',encoding='utf-8') as f:
    print(max(len(line) for line in f))# 选出最长一行
    print(sum(len(line) for line in f))
    info=[line.split() for line in f]
    print(info)

四、递归

items=[1,[2,[3,[4,[5,[6,[7,[8,[9,[0,]]]]]]]]]]
def tell(l):
    for item in l:
        if type(item) is not list:
            print(item)
        else:
            tell(item)
tell(items)

def age(n):
    if n==1:
        return 18
    return age(n-1)+2

print(age(5))#26

def age(n):
    return 18 if n==1 else age(n-1)+2
print(age(5))#26

def foo():
    print('from foo')
    foo()
foo()#递归报错，超过最大限制

五、匿名函数

f=lambda x,n:x**n
print(f)
print(f(2,4))
print(3^6)

六、内置函数

salaries={
    'aa':1200,
    'bb':342,
    'cc':3456,
    'dd':3455
}
def get(k):
    return salaries[k]
print(max(salaries,key=get))#key必须是个函数，该函数必须有返回值

#max()
print(max(salaries,key=lambda k:salaries[k]))

#min()
print(min(salaries,key=lambda k:salaries[k]))

#sorted()默认升序即从小到大，以列表形式返回
salaries=sorted(salaries,key=lambda k:salaries[k])
print(salaries)
#sorted()降序即从大到小
salaries=sorted(salaries,key=lambda k:salaries[k],reverse=True)
print(salaries)

res=map(lambda k:salaries[k],salaries)#得到map的映射对象,是个迭代器
#print(res.__next__())
print(list(res))

name=['aa','bb','cc']
res=map(lambda x:x+'__nb' if x=='cc' else x+'__sb',name)
print(list(res))#['aa__sb', 'bb__sb', 'cc__nb']

from functools import reduce
l=['it','name','is','mage','mage','is','a','little','dog']
res=reduce(lambda x,y:x+' '+y,l)
print(res)

names=['aa_','bb_','cc*','dd_']
res=filter(lambda x:True if x.endswith('_') else False,names)
print(list(res))

res=filter(lambda x:x.endswith('_'),names)
print(list(res))

num=[1,3,3,65,3,4,6,8,5,65]
res=filter(lambda x:x>22,num)
print(list(res))

print(ord('A'))#65
print(chr(77))#M
print(bytes('大王叫我来巡山',encoding='utf-8'))
#b'\xe5\xa4\xa7\xe7\x8e\x8b\xe5\x8f\xab\xe6\x88\x91\xe6\x9d\xa5\xe5\xb7\xa1\xe5\xb1\xb1'

print(abs(-11))#11
print(all(['a',0,1]))#False
print(any(['a',0,1]))#True
print(ascii('花花世界'))#'\u82b1\u82b1\u4e16\u754c'

print(bin(3))#0b11
print(bool(0))#False
print(callable(int))#True
print(classmethod(int))#<classmethod object at 0x00000166BD7BB278>