- Python3学习(1)-基础篇
- Python3学习(2)-中级篇
- 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
1 f = open('./test.txt','r')#只读模式打开test.txt文件
2 print(f.read())#读取文件的所有内容
3 f.close()#关闭文件- 读取文件内容(安全读取try--finally)
1 try:#添加try异常捕获
2 f = open('./test.txt','r')#只读模式打开test.txt文件
3 print(f.read())#读取文件的所有内容
4 finally:
5 if f:
6 f.close()#关闭文件- 使用with简化读取代码
1 with open('./test.txt','r') as f:
2 print(f.read())
3- 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。
1 import os
2
3 print('Process (%s) starting...' % os.getpid())
4
5 pid = os.fork()
6
7 if pid == 0 :
8 print('I am child process (%s) and my parent is %s' %(os.getpid(),os.getppid()))
9 else:
10 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
1 from multiprocessing import Process
2 import os
3
4 #子进程代码
5 def run_proc(name):
6 print('Run child process %s (%s).'%(name,os.getpid()))
7
8
9 if __name__ == '__main__':
10 print('Parent process %s.' % os.getpid())
11 p = Process(target=run_proc,args = ('test',))
12 print('Child process will start..')
13 #启动子进程
14 p.start()
15 #等待子进程结束后再继续往下运行
16 p.join()
17 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
1 from multiprocessing import Pool
2 import os,time,random
3
4 #子进程代码
5 def long_time_task(name):
6 print('Run task %s (%s).' %(name,os.getpid()))
7 start = time.time()
8 time.sleep(random.random()*3)
9 end = time.time()
10 print('Task %s runs %.2f seconds.' %(name,(end-start)))
11
12
13 if __name__ == '__main__':
14 print('Parent process %s.'%os.getpid())
15 #创建线程池
16 p = Pool(4)
17 for i in range(5):
18 p.apply_async(long_time_task,args=(i,))
19 print('Waiting for all subprocesses done..')
20 p.close()
21 p.join()
22 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
1 import subprocess
2
3 print('$ nslookup www.cnblogs.com')
4 #调用外部
5 r = subprocess.call(['nslookup','www.cnblogs.com'])
6 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
1 from multiprocessing import Process,Queue
2 import os,time,random
3
4 #写数据
5 def write(q):
6 print('Process to write:%s'%os.getpid())
7 for value in ['A','B','C']:
8 print('Put %s to queue.'%value)
9 q.put(value)
10 time.sleep(random.random())
11
12 #读数据
13 def read(q):
14 print('Process to read:%s'%os.getpid())
15 while True:
16 value = q.get(True)
17 print('Get %s from queue.'%value)
18
19
20
21 if __name__ == '__main__':
22 q = Queue()
23 pw = Process(target = write,args=(q,))
24 pr = Process(target = read,args=(q,))
25 pw.start()
26 pr.start()
27 pw.join()
28 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。
1 import time,threading
2
3 #线程代码
4 def loop():
5 print('thread %s is running..'%threading.current_thread().name)
6 n = 0
7 while n < 5:
8 n = n + 1
9 print('thread %s >>> %s' %(threading.current_thread().name,n))
10 time.sleep(1)
11 print('thread %s ended.'%threading.current_thread().name)
12
13 print('thread %s is running.'%threading.current_thread().name)
14 t = threading.Thread(target = loop,name = 'LoopThread')
15 t.start()
16 t.join()
17 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.本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
