如何使用Python读取命令行中生成的“错误”内容？

Question

Test is on Linux 32bit. Python 2.7

I want to run this command in Python

 nasm -f elf target.s

and collect the assembly error message this command generates such as these:

target.s:422: error: symbol `loc_8049B1C' undefined
target.s:423: error: symbol `loc_80499E8' undefined
target.s:424: error: symbol `loc_80499AE' undefined

I firstly use this:

infos = subprocess.check_output(["nasm", "-f", "elf", "final.s"], stderr=subprocess.STDOUT)

Python tells me that

subprocess.CalledProcessError: Command '['nasm', '-f', 'elf', 'target.s']' returned non-zero exit status 1

and program terminated

Then I use this:

 infos = os.popen("nasm -f elf target.s").read()

Then infos gets nothing.

So basically could anyone tell me how to get the error message info while keeping the Python program running as normal?

Thank you!

Answer 1

I would use the .communicate() to get the standard error if any.

s = 'nasm -f elf target.s'
proc = subprocess.Popen(s.split(), stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE)
(stdout, stderr) = proc.communicate()
if stderr:
    print stderr

Answer 2

Check output raises a CalledProcessError when the process has a non-zero return status.

The output should be in the output attribute of the exception object.

try:
  infos = subprocess.check_output(["nasm", "-f", "elf", "final.s"], stderr=subprocess.STDOUT)
except subprocess.CalledProcessError as e:
  print e.output