python 笔记

 排序

s = 'aaabbc'
set(s)
# {'a', 'b', 'c'}
sorted((s.count(x), x) for x in set(s))
# [(1, 'c'), (2, 'b'), (3, 'a')]

# 排序后索引
>>> lis = [1,2,3,0,1,9,8]
>>> sorted(range(len(lis)), key=lambda k: lis[k])
[3, 0, 4, 1, 2, 6, 5]

deque 

import collections
deque = collections.deque([1,2,3])
deque.append(4)
a = deque.popleft()

heap

# 若item为list或tuple，依次比较item中的每个元素
import heapq
heap = []            # creates an empty heap
heapq.heappush(heap, item) # pushes a new item on the heap
item = heapq.heappop(heap) # pops the smallest item from the heap
item = heap[0]       # smallest item on the heap without popping it
heapq.heapify(heap)           # transforms list into a heap, in-place, in linear time
item = heapq.heapreplace(heap, item) # pops and returns smallest item, and adds
                               # new item; the heap size is unchanged
_heappop_max(heap)
_heapreplace_max(heap, item)
_heapify_max(x)

ascii

chr(97)  # 'a'
ord('a') # 97

二进制

# https://www.cnblogs.com/renke123/p/11029906.html
int('0b1010',2) 
int('1010',2) # 10  
bin(10) # '0b1010'

当前路径

import os, sys
sys.path # list, python环境路径，import路径，自动加入当前.py所在的文件夹路径（第一个元素）
os.getcwd() # 运行命令时的cd路径

类

静态方法：无法访问类属性、实例属性，相当于一个相对独立的方法，跟类其实没什么关系，换个角度来讲，其实就是放在一个类的作用域里的函数而已。

类成员方法：可以访问类属性，无法访问实例属性。上述的变量val1，在类里是类变量，在实例中又是实例变量，所以容易混淆。

class MyClass:
    val1 = 'Value 1'
    def __init__(self):
        self.val2 = 'Value 2'

    @staticmethod
    def staticmd():
        print '静态方法，无法访问val1和val2'

    @classmethod
    def classmd(cls):
        print '类方法，类：' + str(cls) + '，val1：' + cls.val1 + '，无法访问val2的值'

global、nonlocal

num = 1
def fun1():
    global num  # 需要使用 global 关键字声明
    print(num) 
    num = 123
    print(num)
fun1()
print(num)

out：
1
123
123

def fun():
    num = 1
    def outer():
        num = 10
        def inner():
            nonlocal num   # nonlocal关键字声明
            num = 100
            print(num)

        inner()
        print(num)

    outer()
    print(num)
fun()

out：
100
100
1

 自定义排序

a = [1,2,4,3,5]
def compare_personal(x,y):
    pass
a.sort(key= functools.cmp_to_key(compare_personal))
c = sorted(b, key=functools.cmp_to_key(compare_personal))