python学习笔记

获取mac地址

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import uuid   def get_mac_address(): 　　node = uuid.getnode() 　　mac = uuid.UUID(int = node).hex[-12:] 　　return mac

axios对应的fastapi服务端中间件CORSMiddleware

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# -*- coding: UTF-8 -*- from fastapi import FastAPI from starlette.middleware.cors import CORSMiddleware from fastapi.responses import JSONResponse   app = FastAPI()   app.add_middleware(  # 添加中间件     CORSMiddleware,  # CORS中间件类     allow_origins=["*"],  # 允许起源     allow_credentials=True,  # 允许凭据     allow_methods=["*"],  # 允许方法     allow_headers=["*"],  # 允许头部 )   @app.get("/{a}") async def regist(a):     print('前端数据是：', a)     # print(type(a))     return a

　　

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1、使用 f-string拼接字符串 def manual_str_formatting(name, subscribers):     # better     if subscribers > 100000:         print(f"Wow {name}! you have {subscribers} subscribers!")     else:         print(f"Lol {name} that's not many subs")   2、使用上下文管理器 def finally_instead_of_context_manager(host, port):     # close even if exception     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:         s.connect((host, port))         s.sendall(b'Hello, world')   def manually_calling_close_on_a_file(filename):     with open(filename) as f:         f.write("hello!\n")     # close automatic, even if exception   3、适当使用推导式 odd_squares = {i: i * i for i in range(10)}   c = [] for i in range(n):     for j in range(n):         ij_entry = sum(a[n * i + k] * b[n * k + j] for k in range(n))         c.append(ij_entry)   4、检查类型 def checking_type_equality():     Point = namedtuple('Point', ['x', 'y'])     p = Point(1, 2)       # probably meant to check if is instance of tuple     if isinstance(p, tuple):         print("it's a tuple")     else:         print("it's not a tuple")   5、判断是否单例 def equality_for_singletons(x):     # better     if x is None:         pass       if x is True:         pass   6、for 循环 def range_len_pattern():     a = [1, 2, 3]     # instead     for v in a:         ... def not_using_dict_items():     d = {"a": 1, "b": 2, "c": 3}     for key, val in d.items():         ...   7、解包元组 mytuple = 1, 2 x, y = mytuple   8、统计耗时 def timing_with_time():    # more accurate     start = time.perf_counter()     time.sleep(1)     end = time.perf_counter()     print(end - start)   9、记录日志使用logging def print_vs_logging():     # versus     # in main     level = logging.DEBUG     fmt = '[%(levelname)s] %(asctime)s - %(message)s'     logging.basicConfig(level=level, format=fmt)       # wherever     logging.debug("debug info")     logging.info("just some info")     logging.error("uh oh :(")   10、尝试使用 numpy def not_using_numpy_pandas():     x = list(range(100))     y = list(range(100))     s = [a + b for a, b in zip(x, y)]   import numpy as np def not_using_numpy_pandas():     # 性能更快     x = np.arange(100)     y = np.arange(100)     s = x + y   11、喜欢 import * from itertools import * count()   from mypackage.nearby_module import awesome_function def main():     awesome_function()

 

 

列表中的所有元素组合成字符串 

 

 

交换变量在c++中，肯定需要一个空变量。但是Python不需要，只需一行，大家看清楚了
>>>a,b=b,a

list comprehension列表推导 就是一个更简短、简洁的创建一个list的方法。
>>> some_list = [1, 2, 3, 4, 5]
>>> another_list = [ x + 1 for x in some_list ]
>>> another_list
[2, 3, 4, 5, 6]

Set Comprehensions集合推导
>>> some_list = [1, 2, 3, 4, 5, 2, 5, 1, 4, 8]
>>> even_set = { x for x in some_list if x % 2 == 0 }
>>> even_set
set([8, 2, 4])

Dict Comprehensions字典推导
>>> d = { x: x % 2 == 0 for x in range(1, 11) }
>>> d
{1: False, 2: True, 3: False, 4: True, 5: False, 6: True, 7: False, 8: True, 9: False, 10: True}

计数时使用Counter计数对象。
这听起来显而易见，但经常被人忘记。对于大多数程序员来说，数一个东西是一项很常见的任务，而且在大多数情况下并不是很有挑战性的事情——这里有几种方法能更简单的完成这种任务。
Python的collections类库里有个内置的dict类的子类，是专门来干这种事情的：
>>> from collections import Counter
>>> c = Counter( hello world )
>>> c
Counter({ l : 3, o : 2, : 1, e : 1, d : 1, h : 1, r : 1, w : 1})
>>> c.most_common(2)
[( l , 3), ( o , 2)]

作者：郑子明
链接：https://zhuanlan.zhihu.com/p/442822146
来源：知乎
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

04 漂亮的打印出JSON
JSON是一种非常好的数据序列化的形式，被如今的各种API和web service大量的使用。使用python内置的json处理，可以使JSON串具有一定的可读性，但当遇到大型数据时，它表现成一个很长的、连续的一行时，人的肉眼就很难观看了。
为了能让JSON数据表现的更友好，我们可以使用indent参数来输出漂亮的JSON。当在控制台交互式编程或做日志时，这尤其有用：
>>> import json
>>> print(json.dumps(data)) # No indention
{"status": "OK", "count": 2, "results": [{"age": 27, "name": "Oz", "lactose_intolerant": true}, {"age": 29, "name": "Joe", "lactose_intolerant": false}]}
>>> print(json.dumps(data, indent=2)) # With indention
同样，使用内置的pprint模块，也可以让其它任何东西打印输出的更漂亮。

07 连接
下面的最后一种方式在绑定两个不同类型的对象时显得很cool。
nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
print nfc + afc
>>> [ Packers , 49ers , Ravens , Patriots ]
print str(1) + " world"
>>> 1 world
print `1` + " world"
>>> 1 world
print 1, "world"
>>> 1 world
print nfc, 1
>>> [ Packers , 49ers ] 1

08 数值比较
这是我见过诸多语言中很少有的如此棒的简便法
x = 2
if 3 > x > 1:
print x
>>> 2
if 1 < x > 0:
print x
>>> 2

09 拉链迭代两个列表
nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
for teama, teamb in zip(nfc, afc):
print teama + " vs. " + teamb
>>> Packers vs. Ravens
>>> 49ers vs. Patriots

10 带索引的列表迭代
teams = ["Packers", "49ers", "Ravens", "Patriots"]
for index, team in enumerate(teams):
print index, team
>>> 0 Packers
>>> 1 49ers
>>> 2 Ravens
>>> 3 Patriots

11 列表推导式
已知一个列表，我们可以刷选出偶数列表方法：
numbers = [1,2,3,4,5,6]
even = [number for number in numbers if number%2 == 0]

12 字典推导
和列表推导类似，字典可以做同样的工作：
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print {key: value for value, key in enumerate(teams)}
>>> { 49ers : 1, Ravens : 2, Patriots : 3, Packers : 0}

13 初始化列表的值
items = [0]*3
print items
>>> [0,0,0]

14 列表转换为字符串
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print ", ".join(teams)
>>> Packers, 49ers, Ravens, Patriots

15 从字典中获取元素
我承认try/except代码并不雅致，不过这里有一种简单方法，尝试在字典中找key，如果没有找到对应的alue将用第二个参数设为其变量值。
data = { user : 1, name : Max , three : 4}
is_admin = data.get( admin , False)

17 迭代工具
和collections库一样，还有一个库叫itertools，对某些问题真能高效地解决。其中一个用例是查找所有组合，他能告诉你在一个组中元素的所有不能的组合方式
from itertools import combinations
teams = ["Packers", "49ers", "Ravens", "Patriots"]
for game in combinations(teams, 2):
print game
>>> ( Packers , 49ers )
>>> ( Packers , Ravens )
>>> ( Packers , Patriots )
>>> ( 49ers , Ravens )
>>> ( 49ers , Patriots )
>>> ( Ravens , Patriots )