Update subprocess2.check_output() to behave like subprocess.check_output().

subprocess2.py

 # coding=utf8
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """Collection of subprocess wrapper functions.
 
 In theory you shouldn't need anything else in subprocess, or this module failed.
 """
 
 from __future__ import with_statement
@@ skipping 231 matching lines @@
     # Now that the process died, reset the cursor and read the file.
     buff.seek(0)
     out = [buff.read(), None]
   return out, proc.returncode
 
 
 def call(args, **kwargs):
   """Emulates subprocess.call().
 
   Automatically convert stdout=PIPE or stderr=PIPE to VOID.
+  In no case they can be returned since no code path raises
+  subprocess2.CalledProcessError.
   """
   if kwargs.get('stdout') == PIPE:
     kwargs['stdout'] = VOID
   if kwargs.get('stderr') == PIPE:
     kwargs['stderr'] = VOID
   return communicate(args, **kwargs)[1]
 
 
 def check_call_out(args, **kwargs):
   """Improved version of subprocess.check_call().
@@ skipping 12 matching lines @@
   check_call_out(args, **kwargs)
   return 0
 
 
 def capture(args, **kwargs):
   """Captures stdout of a process call and returns it.
 
   Returns stdout.
 
   - Discards returncode.
-  - Discards stderr. By default sets stderr=STDOUT.
-  - Blocks stdin by default since no output will be visible.
+  - Blocks stdin by default if not specified since no output will be visible.
   """
-  if kwargs.get('stdin') is None:
-    kwargs['stdin'] = VOID
-  if kwargs.get('stdout') is None:
-    kwargs['stdout'] = PIPE
-  if kwargs.get('stderr') is None:
-    kwargs['stderr'] = STDOUT
-  return communicate(args, **kwargs)[0][0]
+  kwargs.setdefault('stdin', VOID)
+
+  # Like check_output, deny the caller from using stdout arg.
+  return communicate(args, stdout=PIPE, **kwargs)[0][0]
 
 
 def check_output(args, **kwargs):
   """Emulates subprocess.check_output().
 
   Captures stdout of a process call and returns stdout only.
 
-  - Discards stderr. By default sets stderr=STDOUT.
   - Throws if return code is not 0.
   - Works even prior to python 2.7.
-  - Blocks stdin by default since no output will be visible.
+  - Blocks stdin by default if not specified since no output will be visible.
+  - As per doc, "The stdout argument is not allowed as it is used internally."
   """
-  if kwargs.get('stdin') is None:
-    kwargs['stdin'] = VOID
-  if kwargs.get('stdout') is None:
-    kwargs['stdout'] = PIPE
-  if kwargs.get('stderr') is None:
-    kwargs['stderr'] = STDOUT
-  return check_call_out(args, **kwargs)[0]
+  kwargs.setdefault('stdin', VOID)
+  return check_call_out(args, stdout=PIPE, **kwargs)[0]