python3中内置函数介绍

from collections import Iterator
test_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
f = filter(lambda x: x % 3 == 0, test_list)
# filter 得到的是一个迭代器

print(isinstance(f, Iterator))
f.__next__()

for i in f:
    print(i)

#输出

True
6
9

from collections import Iterator


def f(x):
    return 2 * x  # 定义一个函数

t_list = [1, 2, 3, 4, 5]

function = map(f, t_list)

print(isinstance(function, Iterator))
# print(function.__next__())
function.__next__()
for i in function:
    print(i)

#输出
True
4
6
8
10

from functools import reduce

f = reduce(lambda x, y: x*y, [1, 2, 4])

print(f)

#输出
8

>>> hex(23)
'0x17'

>>> from collections import Iterator
>>> isinstance(range(5),Iterator)
False
>>> from collections import Iterable
>>> isinstance(range(5),Iterable)
True

>>> f.__next__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'range' object has no attribute '__next__'
>>> for i in f:
...     print(i)
...
0
1
2
3
4

# range(x) 是一个可迭代对象，而不是一个迭代器

>>> list((1,2,3,4,5))   #把一个元组转换为一个列表
[1, 2, 3, 4, 5]

>>> a = [1,2,3,4,5,6]
>>> a[slice(1,3)]
[2, 3]
>>> a[1:3]
[2, 3]

>>> sorted([5,3,2,6,8])
[2, 3, 5, 6, 8]
>>> a = {1:5,6:8,3:6}
>>> sorted(a)  #默认是按key排序
[1, 3, 6]
>>> sorted(a.items())  #按key排序
[(1, 5), (3, 6), (6, 8)]
>>> sorted(a.items(),key = lambda x:x[1])  #按value排序
[(1, 5), (3, 6), (6, 8)]

 a = [1,2,4,5,3,7]
 a.reverse()
a
[7, 3, 5, 4, 2, 1]