--python基础

isinstance判断类型
list(range(100)[::-10])=[99, 89, 79, 69, 59, 49, 39, 29, 19, 9]
s[::-1]和''.join(reversed(s))可以将字符串反转
requests::::get:pramas/auth;post:data;json:json
requests.get(url,timeout=3)
要读取非UTF-8编码的文本文件，需要给open()函数传入encoding参数，例如，读取GBK编码的文件：
>>> f = open('/Users/michael/gbk.txt', 'r', encoding='gbk'，errors='ignore')
>>> f.read()
'测试'
open()函数还接收一个errors参数，表示如果遇到编码错误后如何处理
os.mkdir/rmdir()创建/删除文件夹
os.getcwd()取当前位置
os.path.join/split()拼接/分解地址
os.path.splitext()可以直接让你得到文件扩展名，很多时候非常方便：
os.rename('test.txt', 'test.py')重命名文件/文件夹，更改目录的话会移动文件/文件夹
os.remove('test.py')删除文件/文件夹
shutil.copyfile('f1.log', 'f2.log')复制文件f1到f2
    def f(cd):       遍历cd下的文件和文件夹
        for i in os.listdir(cd):
            if os.path.isfile(os.path.join(cd,i)):
                print('文件',os.path.join(cd,i))
            else:
                print(os.path.join(cd,i))
                f(os.path.join(cd,i))
>>> import json
>>> d = dict(name='Bob', age=20, score=88)
>>> json.dumps(d)
'{"age": 20, "score": 88, "name": "Bob"}'
>>> json_str = '{"age": 20, "score": 88, "name": "Bob"}'
>>> json.loads(json_str)
{'age': 20, 'score': 88, 'name': 'Bob'}
from multiprocessing import Process                          不知道为什么要在cmd运行，否则不显示
import os
# 子进程要执行的代码
def run_proc(name):
    print('Run child process %s (%s)...' % (name, os.getpid()))
if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Process(target=run_proc, args=('test',))
    print('Child process will start.')
    p.start()
    p.join()
    print('Child process end.')
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from multiprocessing import Pool
import os, time, random

def long_time_task(name):
    print('Run task %s (%s)...' % (name, os.getpid()))
    start = time.time()
    time.sleep(random.random() * 3)
    end = time.time()
    print('Task %s runs %0.2f seconds.' % (name, (end - start)))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Pool(4)
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print('Waiting for all subprocesses done...')
    p.close()
    p.join()
    print('All subprocesses done.')
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nultiprocessing/subprocess(popen,queue,call等看不懂)，分布式看不懂
=======================================================================
import time, threading
bb=0
lock=threading.Lock()      建立线程锁对象
def j(n):
    global bb
    lock.acquire()     	线程锁
    try:
        for i in range(100000):       
            bb+=n
            bb-=n
    finally:lock.release()  		 解锁
if __name__=='__main__':
    pp=[]
    for i in range(1,5):
        p=threading.Thread(target=j,args=(i,))
        pp.append(p)
    for i in pp:
        i.setDaemon(True)
        i.start()
    for i in pp:
        i.join()
    print(bb)
====================================================
import time, threading
lo=threading.local()        #交换各线程的局部变量
def f(n):
    n=n**2
    lo.nn=n
    print(threading.current_thread().name,lo.nn)
tt=[]    
for _ in range(9):
    t=threading.Thread(target=f,args=(_,))
    t.setDaemon(True)
    t.start()
    tt.append(t)
for _ in tt:
    _.join()
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