don't use subprocess.check_output

This function was added in Python 2.7 and we're currently targetting 2.6 as a
minimum version. Replaced with a function in util.

beets/util/__init__.py

@@ -22,6 +22,7 @@ import shutil
 import fnmatch
 from collections import defaultdict
 import traceback
+import subprocess
 
 MAX_FILENAME_LENGTH = 200
 WINDOWS_MAGIC_PREFIX = u'\\\\?\\'
@@ -573,3 +574,20 @@ def cpu_count():
         return num
     else:
         return 1
+
+def command_output(cmd):
+    """Wraps the `subprocess` module to invoke a command (given as a
+    list of arguments starting with the command name) and collect
+    stdout. The stderr stream is ignored. May raise
+    `subprocess.CalledProcessError` or an `OSError`.
+
+    This replaces `subprocess.check_output`, which isn't available in
+    Python 2.6 and which can have problems if lots of output is sent to
+    stderr.
+    """
+    with open(os.devnull, 'w') as devnull:
+        proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=devnull)
+        stdout, _ = proc.communicate()
+    if proc.returncode:
+        raise subprocess.CalledProcessError(proc.returncode, cmd)
+    return stdout

beets/util/artresizer.py

@@ -20,6 +20,7 @@ import subprocess
 import os
 from tempfile import NamedTemporaryFile
 import logging
+from beets.util import command_output
 
 # Resizing methods
 PIL = 1
@@ -42,8 +43,7 @@ def call(args):
     command exits abnormally, a ArtResizerError is raised.
     """
     try:
-        with open(os.devnull, 'w') as devnull:
-            return subprocess.check_output(args, stderr=devnull)
+        return command_output(args)
     except subprocess.CalledProcessError as e:
         raise ArtResizerError(
             "{0} exited with status {1}".format(args[0], e.returncode)

beetsplug/convert.py

@@ -21,7 +21,7 @@ import threading
 from subprocess import Popen, PIPE
 
 from beets.plugins import BeetsPlugin
-from beets import ui, library, util
+from beets import ui, util
 from beetsplug.embedart import _embed
 
 log = logging.getLogger('beets')

beetsplug/replaygain.py

@@ -18,7 +18,7 @@ import os
 
 from beets import ui
 from beets.plugins import BeetsPlugin
-from beets.util import syspath
+from beets.util import syspath, command_output
 from beets.ui import commands
 
 log = logging.getLogger('beets')
@@ -30,13 +30,11 @@ class ReplayGainError(Exception):
     """
 
 def call(args):
-    """Execute the command indicated by `args` (a list of strings) and
-    return the command's output. The stderr stream is ignored. If the
-    command exits abnormally, a ReplayGainError is raised.
+    """Execute the command and return its output or raise a
+    ReplayGainError on failure.
     """
     try:
-        with open(os.devnull, 'w') as devnull:
-            return subprocess.check_output(args, stderr=devnull)
+        return command_output(args)
     except subprocess.CalledProcessError as e:
         raise ReplayGainError(
             "{0} exited with status {1}".format(args[0], e.returncode)