Python3学习(3)-高级篇

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

先从io中引入StringIO
创建一个StringIO对象
写字符串到StringIO对象f中
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

从io中引入BytesIO
创建一个BytesIO对象
写字节对象
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'\xe6\x88\x91\xe6\x98\xaf\xe4\xb8\xad\xe6\x96\x87'

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.

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Python3学习(3)-高级篇

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