Python3學習(3)-高級篇

 

• Python3學習(1)-基礎篇
• Python3學習(2)-中級篇
• Python3學習(3)-高級篇

 

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• 文件讀寫
  • 源文件test.txt

  • line1
    line2
    line3

  • 讀取文件內容

  • f = open('./test.txt','r')#只讀模式打開test.txt文件
    print(f.read())#讀取文件的所有內容
    f.close()#關閉文件

  • 讀取文件內容(安全讀取try--finally)

  • try:#添加try異常捕獲
        f = open('./test.txt','r')#只讀模式打開test.txt文件
        print(f.read())#讀取文件的所有內容
    finally:
        if f:    
            f.close()#關閉文件

  • 使用with簡化讀取代碼

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

  • 以上所有的執行結果均為

  • ➜  Python  python3 readTxt.py
    line1
    line2
    line3

  • 讀取方法詳解
    • read():讀取文件的所有內容。針對小文件
    • read(size):按指定大小來讀取文件的內容。size字節大小。針對大文件
    • readlines():按行來讀取文件的所有內容，返回為list格式。針對配制文件
  • 讀取模式
    • 'r'：讀文件
    • 'rb'：二進制讀文件
    • 'w'：寫文件
    • 'wb'：二進制寫文件
• StringIO、BytesIO
  • StringIO:字符串IO
    1.  先從io中引入StringIO
    2. 創建一個StringIO對象
    3. 寫字符串到StringIO對象f中
    4. 獲取字符串內容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.  從io中引入BytesIO
    2. 創建一個BytesIO對象
    3. 寫字節對象
    4. 獲取寫入的字節內容內容

    • >>> from io import BytesIO
      >>> f = BytesIO()
      >>> f.write('我是中文'.encode('utf-8'))
      12
      >>> print(f.getvalue())
      b'\xe6\x88\x91\xe6\x98\xaf\xe4\xb8\xad\xe6\x96\x87'

• 多進程
  • fork()
    • fork()調用一次，返回兩次，因為操作系統自動把當前進程（稱為父進程）復制了一份（稱為子進程），然后，分別在父進程和子進程內返回。
    • 子進程永遠返回0，而父進程返回子進程的ID。這樣做的理由是，一個父進程可以fork出很多子進程，所以，父進程要記下每個子進程的ID，而子進程只需要調用getppid()就可以拿到父進程的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
      
      #子進程代碼
      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..')
          #啟動子進程
          p.start()
          #等待子進程結束后再繼續往下運行
          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線程池

    • from multiprocessing import Pool
      import os,time,random
      
      #子進程代碼
      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())
          #創建線程池
          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.

  • 子進程
    • 調用外部進程(系統進程):nslookup
    • 使用子進程

    • import subprocess
      
      print('$ nslookup www.cnblogs.com')
      #調用外部
      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查看結果

    • ➜  ~  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

  • 多進程數據通信
    • 一個向Queue中寫數據，另一外讀數據

    • from multiprocessing import Process,Queue
      import os,time,random
      
      #寫數據
      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())
      
      #讀數據
      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.

  • 選擇
    • Unix/Linux下可使用fork()
    • 跨平台使用multiprocessing
    • 多進程數據通信Queue、Pipes
• 多線程
  • 進程是由若干線程組成的，一個進程至少有一個線程。

    • import time,threading
      
      #線程代碼
      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.