Python3学习(3)-高级篇

• Python3学习(1)-基础篇
• Python3学习(2)-中级篇
• Python3学习(3)-高级篇

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• 文件读写
  • 源文件test.txt

  • line1
    line2
    line3

  • 读取文件内容

  • f = open('./test.txt','r')#只读模式打开test.txt文件
    print(f.read())#读取文件的所有内容
    f.close()#关闭文件

  • 读取文件内容(安全读取try--finally)

  • try:#添加try异常捕获
        f = open('./test.txt','r')#只读模式打开test.txt文件
        print(f.read())#读取文件的所有内容
    finally:
        if f:    
            f.close()#关闭文件

  • 使用with简化读取代码

  • with open('./test.txt','r') as f:
        print(f.read())
        

  • 以上所有的执行结果均为

  • ➜  Python  python3 readTxt.py
    line1
    line2
    line3

  • 读取方法详解
    • read():读取文件的所有内容。针对小文件
    • read(size):按指定大小来读取文件的内容。size字节大小。针对大文件
    • readlines():按行来读取文件的所有内容，返回为list格式。针对配制文件
  • 读取模式
    • 'r'：读文件
    • 'rb'：二进制读文件
    • 'w'：写文件
    • 'wb'：二进制写文件
• StringIO、BytesIO
  • StringIO:字符串IO
    1.  先从io中引入StringIO
    2. 创建一个StringIO对象
    3. 写字符串到StringIO对象f中
    4. 获取字符串内容f.getvalue()

    • >>> from io import StringIO
      >>> f  = StringIO()
      >>> f.write('hello')
      5
      >>> f.write(' ')
      1
      >>> f.write('world!')
      6
      >>> print(f.getvalue())
      hello world!

  • BytesIO
    1.  从io中引入BytesIO
    2. 创建一个BytesIO对象
    3. 写字节对象
    4. 获取写入的字节内容内容

    • >>> from io import BytesIO
      >>> f = BytesIO()
      >>> f.write('我是中文'.encode('utf-8'))
      12
      >>> print(f.getvalue())
      b'xe6x88x91xe6x98xafxe4xb8xadxe6x96x87'

• 多进程
  • fork()
    • fork()调用一次，返回两次，因为操作系统自动把当前进程（称为父进程）复制了一份（称为子进程），然后，分别在父进程和子进程内返回。
    • 子进程永远返回0，而父进程返回子进程的ID。这样做的理由是，一个父进程可以fork出很多子进程，所以，父进程要记下每个子进程的ID，而子进程只需要调用getppid()就可以拿到父进程的ID。

    • import os
      
      print('Process (%s) starting...' % os.getpid())
      
      pid = os.fork()
      
      if pid == 0 :
          print('I am child process (%s) and my parent is %s' %(os.getpid(),os.getppid()))
      else:
          print('I (%s) just created a child process (%s)' %(os.getpid(),pid))

    • ➜  Python  python3 ThreadDemo.py
      Process (711) starting...
      I (711) just created a child process (712)
      I am child process (712) and my parent is 711

  • multiprocessing－Process

    • from multiprocessing import Process
      import os
      
      #子进程代码
      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..')
          #启动子进程
          p.start()
          #等待子进程结束后再继续往下运行
          p.join()
          print('Child process end.')

    • ➜  Python  python3 MultiProcessins.py
      Parent process 718.
      Child process will start..
      Run child process test (719).
      Child process end.

  • Pool线程池

    • from multiprocessing import Pool
      import os,time,random
      
      #子进程代码
      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 %.2f seconds.' %(name,(end-start)))
      
      
      if __name__ == '__main__':
          print('Parent process %s.'%os.getpid())
          #创建线程池
          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.')

    • ➜  Python  python3 Pool.py
      Parent process 730.
      Waiting for all subprocesses done..
      Run task 0 (731).
      Run task 1 (732).
      Run task 2 (733).
      Run task 3 (734).
      Task 2 runs 0.18 seconds.
      Run task 4 (733).
      Task 3 runs 0.83 seconds.
      Task 0 runs 1.18 seconds.
      Task 4 runs 2.46 seconds.
      Task 1 runs 2.66 seconds.
      All subprocesses done.

  • 子进程
    • 调用外部进程(系统进程):nslookup
    • 使用子进程

    • import subprocess
      
      print('$ nslookup www.cnblogs.com')
      #调用外部
      r = subprocess.call(['nslookup','www.cnblogs.com'])
      print('Exit code:',r)

      ➜  Python  python3 SubProcess.py
      $ nslookup www.cnblogs.com
      Server:		10.1.1.5
      Address:	10.1.1.5#53
      
      Non-authoritative answer:
      Name:	www.cnblogs.com
      Address: 42.121.252.58
      
      Exit code: 0

    • 直接使用nslookup查看结果

    • ➜  ~  nslookup www.cnblogs.com
      Server:		10.1.1.5
      Address:	10.1.1.5#53
      
      Non-authoritative answer:
      Name:	www.cnblogs.com
      Address: 42.121.252.58

  • 多进程数据通信
    • 一个向Queue中写数据，另一外读数据

    • from multiprocessing import Process,Queue
      import os,time,random
      
      #写数据
      def write(q):
          print('Process to write:%s'%os.getpid())
          for value in ['A','B','C']:
              print('Put %s to queue.'%value)
              q.put(value)
              time.sleep(random.random())
      
      #读数据
      def read(q):
          print('Process to read:%s'%os.getpid())
          while True:
              value = q.get(True)
              print('Get %s from queue.'%value)
      
      
      
      if __name__ == '__main__':
          q = Queue()
          pw = Process(target = write,args=(q,))
          pr = Process(target = read,args=(q,))
          pw.start()
          pr.start()
          pw.join()
          pr.terminate()

    • ➜  Python  python3 ProcessConn.py
      Process to write:803
      Put A to queue.
      Process to read:804
      Get A from queue.
      Put B to queue.
      Get B from queue.
      Put C to queue.
      Get C from queue.

  • 选择
    • Unix/Linux下可使用fork()
    • 跨平台使用multiprocessing
    • 多进程数据通信Queue、Pipes
• 多线程
  • 进程是由若干线程组成的，一个进程至少有一个线程。

    • import time,threading
      
      #线程代码
      def loop():
          print('thread %s is running..'%threading.current_thread().name)
          n = 0
          while n < 5:
              n = n + 1
              print('thread %s >>> %s' %(threading.current_thread().name,n))
              time.sleep(1)
          print('thread %s ended.'%threading.current_thread().name)
      
      print('thread %s is running.'%threading.current_thread().name)
      t = threading.Thread(target = loop,name = 'LoopThread')
      t.start()
      t.join()
      print('thread %s ended.'%threading.current_thread().name)

    • ➜  Python  python3 Thread.py
      thread MainThread is running.
      thread LoopThread is running..
      thread LoopThread >>> 1
      thread LoopThread >>> 2
      thread LoopThread >>> 3
      thread LoopThread >>> 4
      thread LoopThread >>> 5
      thread LoopThread ended.
      thread MainThread ended.