python----常用功能

sintance和type

class Foo(object):
    pass

class Bar(Foo):
    pass

obj = Bar()
# isinstance用于判断，对象是否是指定类的实例 （错误的）
# isinstance用于判断，对象是否是指定类或其派生类的实例
# isinstance不精准
print(isinstance(obj,Foo),id(obj))   #True 35558624
print(isinstance(obj,Bar),id(obj))   #True 35558624

print(type(obj)==Foo)  #False
print(type(obj)==Bar)  #True

json

import json
v = {"name":"海燕","age":22}
str_dic = json.dumps(v)
print(json.dumps(v),type(str_dic))  #{"name": "u6d77u71d5", "age": 22}<class 'str'>
print(json.dumps(v,ensure_ascii=False))  #{"name": "海燕", "age": 22}

OrderedDict   

使用字典时，key是无序的。在对字典做迭代时，我们无法确定key的顺序。如果要保持key的顺序，可以用OrderedDict

from collections import OrderedDict
od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])
for i in od.keys():
    print(i)

Counter 

计数器

from collections import Counter
c = Counter('abcdeabcdabcaba')
print(c["a"])  #5

defaultdict

from  collections import defaultdict
values = [11,22,33,44,55,66,77,88,99]
my_dict = defaultdict(list)
for v in values:
    if v>66:
        my_dict['k1'].append(v)
print(my_dict)

模拟defaultdict

values = [11,22,33,44,55,66,77,88,99]
my_dict = {}
for v in values:
    if v>66:
        if "k1" in  my_dict.keys():
            my_dict['k1'].append(v)
        else:
            my_dict["k1"]=[]
            my_dict['k1'].append(v)
print(my_dict)

deque

是为了高效实现插入和删除操作的双向队列，适用于队列和栈

from collections import deque
q = deque(['a','b','c'])
q.append('ee')#添加元素
q.append('ff')
q.append('qq')
print(q)
q.appendleft('www')#从左边添加
print(q)

q.pop() #删除元素
q.popleft() #从左边删除元素
print(q)

元祖的排序

anwsers = [(1,2),(3,2),(2,2)]
x = sorted(anwsers,key=lambda x:x[0],reverse=True)
print(x)