python3中的CalledProcessError之後的子進程輸出

Question

我試圖在Python中使用subprocess來運行bandit。我有一些像這樣的代碼：

import subprocess 

command = ['bandit', '-r', 'goodcode'] 
output = subprocess.check_output(command) 
print(output.decode()) 

這工作得很好，並給我一個字符串輸出是這樣的：

Run started:2016-09-27 10:37:17.567678 

Test results: 
     No issues identified. 

Code scanned: 
     Total lines of code: 940 
     Total lines skipped (#nosec): 0 

Run metrics: 
     Total issues (by severity): 
       Undefined: 0 
       Low: 0 
       Medium: 0 
       High: 0 
     Total issues (by confidence): 
       Undefined: 0 
       Low: 0 
       Medium: 0 
       High: 0 
Files skipped (0): 

...然而，當我在一個目錄下運行，其中bandit返回一些錯誤，bandit過程本身返回1。因此，我必須抓住CalledProcessError像這樣：

import subprocess 

command = ['bandit', '-r', 'badcode'] 

try: 
    output = subprocess.check_output(command) 
except subprocess.CalledProcessError as e: 
    output = e.output 

print(output.decode()) 

...使我有以下結果：

b"Run started:2016-09-27 10:42:26.616123\n\nTest results:\n>> Issue: [B110:try_except_pass] Try, Except, Pass detected.\n Severity: Low Confidence: High\n Location: badcode/conf/settings_development.py:93\n92\t from .settings_local import *\n93\texcept:\n94\t pass\n\n--------------------------------------------------\n>> Issue: [B105:hardcoded_password_string] Possible hardcoded password: 'password'\n Severity: Low Confidence: Medium\n Location: badcode/frontend/tests/test_views.py:21\n20\t  form['username'] = self.user.username\n21\t  form['password'] = 'password'\n22\t\n\n--------------------------------------------------\n>> Issue: [B105:hardcoded_password_string] Possible hardcoded password: 'password'\n Severity: Low Confidence: Medium\n Location: badcode/frontend/tests/test_views.py:35\n34\t  form['username'] = self.user.username\n35\t  form['password'] = 'password'\n36\t\n\n--------------------------------------------------\n>> Issue: [B110:try_except_pass] Try, Except, Pass detected.\n Severity: Low Confidence: High\n Location: badcode/reasons/views.py:234\n233\t    nr = subject.number\n234\t   except:\n235\t    pass\n\n--------------------------------------------------\n>> Issue: [B110:try_except_pass] Try, Except, Pass detected.\n Severity: Low Confidence: High\n Location: badcode/reasons/views.py:277\n276\t    nr = event.number\n277\t   except:\n278\t    pass\n\n--------------------------------------------------\n>> Issue: [B110:try_except_pass] Try, Except, Pass detected.\n Severity: Low Confidence: High\n Location: badcode/retention/migrations/0010_auto_20160527_1603.py:13\n12\t   retention.save()\n13\t  except:\n14\t   pass\n\n--------------------------------------------------\n>> Issue: [B110:try_except_pass] Try, Except, Pass detected.\n Severity: Low Confidence: High\n Location: badcode/retention/migrations/0015_auto_20160623_1051.py:13\n12\t   retention.save()\n13\t  except:\n14\t   pass\n\n--------------------------------------------------\n>> Issue: [B108:hardcoded_tmp_directory] Probable insecure usage of temp file/directory.\n Severity: Medium Confidence: Medium\n Location: badcode/utils/views.py:322\n321\t  css = '{}/static/badcode/css/screen.css'.format(settings.ROOT_DIR)\n322\t  location = '/tmp/{}.pdf'.format(filename)\n323\t\n\n--------------------------------------------------\n\nCode scanned:\n\tTotal lines of code: 15287\n\tTotal lines skipped (#nosec): 0\n\nRun metrics:\n\tTotal issues (by severity):\n\t\tUndefined: 0.0\n\t\tLow: 7.0\n\t\tMedium: 1.0\n\t\tHigh: 0.0\n\tTotal issues (by confidence):\n\t\tUndefined: 0.0\n\t\tLow: 0.0\n\t\tMedium: 3.0\n\t\tHigh: 5.0\nFiles skipped (0):\n" 

注意，b""是字符串裏面，所以output[0] == 'b'和output[1] == '"'。爲什麼是這樣？如果進程已經返回0，e.output不應該編碼輸出與output相同嗎？

Answer 1

看起來你已經看過output變量，然後在第二種情況下調用.decode()方法。在兩種情況下，output引用相同的字節串。

>>> import subprocess, sys 
>>> output1 = subprocess.check_output([sys.executable, '-c', 'print("abc")']) 
>>> try: 
... subprocess.check_output([sys.executable, '-c', 
...       'print("abc"); import sys;sys.exit(1)']) 
... except subprocess.CalledProcessError as e: 
... output2 = e.output 
... 
>>> output1 == output2 
True 

如果非零退出狀態是不是在你的情況的錯誤，那麼你可以使用不在這種情況下提高CalledProcessError功能：

#!/usr/bin/env python3 
from subprocess import run, PIPE 

finished_process = run(command, stdout=PIPE, universal_newlines=True) 
print("{p.returncode}, {p.stdout}".format(p=finished_process)) 
# e.g.: 1, abc 

universal_newlines=True是「一個不起眼的拼寫啓用文本模式「。