python学习day16 内置函数二

# 数据类型：int bool float等等
# 数据结构：dict tuple list set str

# 内置函数
# l =[1,2,3,4,5]
# l.reverse()
# print(l)
# l = [1,2,3,4,5]
# l2 = reversed(l)    #保留原列表，返回一个反向的迭代器
# print(l2)

# l = [1,2,3,4,5,6,7,8,9]
# sli = slice(1,5,2)
# print(l[sli])   #切片函数

# print(format('text','<20')) #左对齐
# print(format('text','>20')) #右对齐
# print(format('text','^20')) #居中

# bytes--转换成bytes类型
# 拿到的是gbk编码，想转化成utf-8编码
# 运用范围：
# 网络编程
# 照片和视频
# html爬取到的内容
# print(bytes('你好',encoding='gbk')) #unicode转换成gbk的bytes
# print(bytes('你好',encoding='utf-8'))   #unicode转换成utf-8的bytes

# b_array = bytearray('你好',encoding='utf-8')
# print(b_array)  #转换成字节类型的数组
# print(b_array[0])

# print(ord('好')) #返回ascii或unicode值
# print(ord('a'))

# print(ascii('a'))
# print(ascii('豪'))

# name = 'egg'
# print('你好%r'%name)
# print(repr('dfasfd'))

# print(all(['a',1,45,6,67,0]))   #判断是否全部为True
# print(any(['a',1,45,6,67,0]))   #判断是否有一个为True

# zip（）拉链方法
# l=[1,2,3,4,5]
# l2=['a','b','c']
# l3=['*','**','&&']
# l4={'k1':3,'k2':3,'k3':3}
# ret = zip(l,l2,l3,l4)
# print(ret)  #返回一个迭代器
# for i in ret:
#     print(i)    #返回的是一个元组

# filter（function, iterable）过滤函数
# def is_odd(x):
#     return x%2 == 1
# ret = filter(is_odd,[1,2,3,4,5,6])  #返回迭代器
# for i in ret:
#     print(i)
# 其实就是列表解析[i for i in [1,2,3,4,5,6] if i%2 == 1]

# def is_srt(s):
#     return s and str(s).strip()
# ret = filter(is_srt,[1,2,3,4,5,'   ','python'])
# for i in ret:
#     print(i)

# l = [1,2,3,4,-43,-5]
# l.sort(key=abs)
# print(l)#在原有的列表上排序，并可指定排序方式

# l = [1,2,3,4,-43,-5]
# print(sorted(l,key=abs,reverse=True)) #生成一个新列表，不改变原有列表但是会占内存
# print(l)

# 小练习：用列表按照每个元素的长度排序
# l = ['dsfds','sdafsdfas','sd']
# new_l = sorted(l,key=len,reverse=True)
# print(new_l)

# 匿名函数--只能写在一行
# def add(x,y):
#     return x+y
# add=lambda x,y:x+y
# print(add(99,1))

# 按照value值进行排序
# dic = {'k1':10,'k2':100,'k3':1000}
# def func(key):
#     return dic[key]
# print(max(dic,key=func))错误
# print(max(dic,key=lambda key:dic[key]))

# ret = map(abs,[-1,-4,4,35])
# for i in ret:
#     print(i)

# def func(x):
#     return x**2
# ret = map(func,[-1,-4,4,35])
# for i in ret:
#     print(i)
# 就等于
# ret = map(lambda x:x**2,[-1,-4,4,35])
# for i in ret:
#     print(i)

# 筛选大于10的数
# res = filter(lambda x:x>10,[23,4,45,65,7,67])
# for i in res:
#     print(i)

# 与lambda连用的内置函数--filter、map、sorted，min，max

# 面试提练习
# 1.下面程序的输出结果是：
# d = lambda p: p * 2
# t = lambda p: p * 3
# x = 2
# x = d(x)    #x=4
# x = t(x)    #x=12
# x = d(x)    #x=24
# print(x)

# 2.现有两元组(('a'),('b')),(('c'),('d')),请使用python中匿名函数生成列表[{'a':'c'},{'b':'d'}]
# ret = zip((('a'),('b')),(('c'),('d')))
# print(list(map(lambda tup:{tup[0]:tup[1]},ret)))
# 3.以下代码的输出是什么？请给出答案并解释。
# def multipliers():
#     return [lambda x:i*x for i in range(4)]
# print([m(2) for m in multipliers()])
# # 请修改multipliers的定义来产生期望的结果。
# def multipliers():
#     return (lambda x:i*x for i in range(4))
# print([m(2) for m in multipliers()])