python - Python subprocess with stdout redirect returning an int

Question

I am trying to read out data from a set of print statements in a C++ program that is being run using a subprocess.

C++ code:

printf "height= %.15f \\ntilt = %.15f \(%.15f\)\\ncen_volume= %.15f\\nr_volume= %.15f\\n", height, abs(sin(tilt*pi/180)*ring_OR), abs(tilt), c_vol, r_vol; e; //e acts like a print

Python code:

run = subprocess.call('Name', stdout = subprocess.PIPE, env={'LANG':'C++'})
data, error = run.communicate()

However instead of getting the data, all I am getting is a single int, the exit code, either a 0 or an error code. Of course, python then tells me "AttributeError: 'int' object has no attribute 'communicate'".

How do I actually get the data (the printf)?

Answer 1

subprocess.call只是运行命令并返回其退出状态（在 python 中，退出状态可以通过sys.exit(N)-- 在其他语言中，退出状态由不同的方式确定）。如果你想真正掌握这个过程，你需要使用subprocess.Popen. 因此，对于您的示例：

run = subprocess.Popen('Name', stdout = subprocess.PIPE, env={'LANG':'C++'})
data, error = run.communicate()

程序退出状态现在可通过该returncode属性获得。

另外，作为风格问题，我会这样做：

run = subprocess.Popen('Name', stdout = subprocess.PIPE, stderr = subprocess.PIPE, env={'LANG':'C++'})
data, error = run.communicate()

或者：

run = subprocess.Popen('Name', stdout = subprocess.PIPE, env={'LANG':'C++'})
data, _ = run.communicate()

既然你没有给自己捕获标准错误的能力，你可能不应该假装你有一些有意义的东西。