python基础一 day16 内置函数

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

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

l = (1,2,23,213,5612,342,43)
sli = slice(1,5,2)
print(l[sli])
print(l[1:5:2])

print(format('test', '<20'))
print(format('test', '>40'))
print(format('test', '^40'))

bytes 转换成bytes类型
我拿到的是gbk编码的，我想转成utf-8编码
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

网络编程 只能传二进制
照片和视频也是以二进制存储
html网页爬取到的也是编码
b_array = bytearray('你好',encoding='utf-8')
print(b_array)
print(b_array[0])
'\xe4\xbd\xa0\xe5\xa5\xbd'
s1 = 'alexa'
s2 = 'alexb'

l = 'ahfjskjlyhtgeoahwkvnadlnv'
l2 = l[:10]

切片 —— 字节类型  不占内存
字节 —— 字符串 占内存

print(ord('好'))
print(ord('1'))
print(chr(97))

print(ascii('好'))
print(ascii('1'))
name = 'egg'
print('你好%r'%name)
print(repr('1'))
print(repr(1))

print(all(['a','',123]))
print(all(['a',123]))
print(all([0,123]))

print(any(['',True,0,[]]))

l = [1,2,3,4,5]
l2 = ['a','b','c','d']
l3 = ('*','**',[1,2])
d = {'k1':1,'k2':2}
for i in zip(l,l2,l3,d):
    print(i)

def is_odd(x):
    return x % 2 == 1

def is_str(s):
    return s and str(s).strip()

ret = filter(is_odd, [1,  6, 7, 12, 17])
ret = filter(is_str, [1, 'hello','','  ',None,[], 6, 7, 'world', 12, 17])
print(ret)
for i in ret:
    print(i)
[i for i in [1, 4, 6, 7, 9, 12, 17] if i % 2 == 1]

from math import sqrt
def func(num):
    res = sqrt(num)
    return res % 1 == 0
ret = filter(func,range(1,101))
for i in ret:
    print(i)


ret = map(abs,[1,-4,6,-8])
print(ret)
for i in ret:
    print(i)


filter 执行了filter之后的结果集合 <= 执行之前的个数
        filter只管筛选，不会改变原来的值
map 执行前后元素个数不变
      值可能发生改变

l = [1,-4,6,5,-10]
# l.sort(key = abs)   # 在原列表的基础上进行排序
# print(l)

print(sorted(l,key=abs,reverse=True))      # 生成了一个新列表 不改变原列表 占内存
print(l)

l = ['   ',[1,2],'hello world']
new_l = sorted(l,key=len)
print(new_l)