一、多進程

1.fork方法（os模塊,適用於Lunix系統）

fork方法：調用1次，返回2次。原因：操作系統經當前進程（父進程）復制出一份進程（子進程），兩個進程幾乎完全相同，fork方法分別在父進程、子進程中返回，子進程返回值為0，父進程中返回的是子進程的ID。

普通方法：調用1次，返回1次

import os

if __name__ == ‘__main__‘:
    print ‘current Process (%s) start ....‘%(os.getpid())        #getpid()用戶獲取當前進程ID
    pid = os.fork()
    if pid <0:
        
 
print ‘error in fork‘
    elif pid == 0:
        print ‘I am child process (%s)‘ and my parent process is (%s)‘,(os.getpid(),os.getppid())
    else:
        print ‘I (%s) created a child process (%s).‘,(os.getpid(),pid)


運行結果如下：
current Process (3052) start ....
I (3052) created a child process (3053).
I am child process (
 
3053) and my parent process is (3052)

2.multiprocessing（跨平臺）

import os

# 從multiprocessing模塊中導入Process類
from multiprocessing import Process

def run_proc(name):
    print ‘Child process %s (%s) Running...‘ % (name,os.getpid())
if __name__ == ‘__main__‘:
    print ‘Parent process %s.‘ % os.getpid()
    
 
for i in range(5):
        p = Process(target = run_proc,args = (str(i),))
        print ‘Process will start‘
        #用於啟動進程
        p.start()
    # 用於實現進程間的同步
    p.join()
    print ‘Process end‘

執行結果如下：
Parent process 2392.
Process will start.
Process will start.
Process will start.
Process will start.
Process will start.
Child process 2 (10748) Runing...
Child process 0 (5324) Runing...
Child process 1 (3196) Runing...
Child process 3 (4680) Runing...
Child process 4 (10696) Runing...
Process end        

python爬蟲【第2篇】