python - 运行子进程时检查条件

Question

我正在使用 subprocess.Popen() 执行命令。我想等待进程完成后再执行其余代码，但同时我想在运行子进程 2 分钟后检查生成的文件的状态。如果文件大小为零，那么我想停止该过程。目前我的代码如下。有没有更聪明的方法来做到这一点？

  def execute(command,outputfilename):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    start_time=time.time()
    Is_Working=False
    while True:
     process.poll()
     if not Is_Working:
         #allow 2 minutes for the process to create results
         if process.returncode == None and (time.time()-start_time)//60>1:
             Is_Working=True
             if (os.stat(outputfilename)[6]==0):
                 process.kill()
                 return
     if process.returncode != None: 
         break

    output, errors=process.communicate()

Answer 1

从全局范围来看，你的代码对我来说看起来不错。仅一些细节:

1. 在 (time.time()-start_time)//60>1 ，我认为//没有什么用处。 ，因为您不一定需要对结果进行取整，并将除法的 lhs 结果转换为整数。保持全部 float 应该可以进行比较，这都是基本的机器逻辑；
2. 您可以通过使用 while process.returncode is not None:… 更改循环条件来避免退出无限循环。
3. 为了更简单，我实际上会循环直到文件大小为 !=0然后调用process.wait()就在循环之后。
4. 这将是使用 while/else 的一个很好的场景构造

因此，一项改进是，您可以在流程完成后(无论成功还是失败)执行一些操作(例如清理或重试...):

def execute(command,outputfilename):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    start_time=time.time()
    Is_Working=False
    while process.returncode == None:
        process.poll()
        #allow 2 minutes for the process to create results
        if (time.time()-start_time)/60 > 1:
            if (os.stat(outputfilename)[6]==0):
                process.kill()
                break
    else:
        # the process has not been killed
        # wait until it finishes
        process.wait()
        output, errors=process.communicate()
        # do stuff with the output
        […]

    # here the process may have been killed or not
    […]

或者另一个好的选择是引发异常:

def execute(command,outputfilename):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    start_time=time.time()
    Is_Working=False
    while process.returncode == None:
        process.poll()
        #allow 2 minutes for the process to create results
        if (time.time()-start_time)/60 > 1:
            if (os.stat(outputfilename)[6]==0):
                process.kill()
                raise Exception("Process has failed to do its job")
    # the process has not been killed
    # wait until it finishes
    process.wait()
    output, errors=process.communicate()
    # do stuff with the output
    […]

HTH