内置函数

reverse()

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

bytes()

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

map,

filter

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

sorted()

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)

 匿名函数

ret = zip((('a'),('b')),(('c'),('d')))
res = map(lambda tup:{tup[0]:tup[1]},ret)
print(list(res))

def multipliers():
    return [lambda x:i*x for i in range(4)]
print([m(2) for m in multipliers()])