use Popen instead of getstatusoutput to check for libedit.

getstatusoutput uses os.popen, and is vulnerable to EINTR weirdness
in environments such as gdb or PyQt.

Exponential falloff is also used, to prevent waiting forever or firing requests too fast, though I haven't had it fire more than once
after moving to Popen.

closes gh-473

IPython/utils/rlineimpl.py

@@ -1,86 +1,95 b''
 # -*- coding: utf-8 -*-
 """ Imports and provides the 'correct' version of readline for the platform.
 
 Readline is used throughout IPython as::
 
     import IPython.utils.rlineimpl as readline
 
 In addition to normal readline stuff, this module provides have_readline
 boolean and _outputfile variable used in IPython.utils.
 """
 
+import re
 import sys
+import time
 import warnings
 
+from subprocess import Popen, PIPE
+
 try:
     from readline import *
     import readline as _rl
     have_readline = True
 except ImportError:
     try:
         from pyreadline import *
         import pyreadline as _rl
         have_readline = True
     except ImportError:
         have_readline = False
 
 if have_readline and hasattr(_rl, 'rlmain'):
     # patch add_history to allow for strings in pyreadline <= 1.5:
     # fix copied from pyreadline 1.6
     import pyreadline
     if pyreadline.release.version <= '1.5':
         def add_history(line):
             """add a line to the history buffer."""
             from pyreadline import lineobj
             if not isinstance(line, lineobj.TextLine):
                 line = lineobj.TextLine(line)
             return _rl.add_history(line)
 
 if sys.platform == 'win32' and have_readline:
     try:
         _outputfile=_rl.GetOutputFile()
     except AttributeError:
         print "Failed GetOutputFile"
         have_readline = False
 
 # Test to see if libedit is being used instead of GNU readline.
-# Thanks to Boyd Waters for this patch.
+# Thanks to Boyd Waters for the original patch.
 uses_libedit = False
 if sys.platform == 'darwin' and have_readline:
-    import commands
-    # Boyd's patch had a 'while True' here, I'm always a little worried about
-    # infinite loops with such code, so for now I'm taking a more conservative
-    # approach. See https://bugs.launchpad.net/ipython/+bug/411599.
-    for i in range(10):
-        try:
-            (status, result) = commands.getstatusoutput( "otool -L %s | grep libedit" % _rl.__file__ )
+    # Previously this used commands.getstatusoutput, which uses os.popen.
+    # Switching to subprocess.Popen, and exponential falloff for EINTR
+    # seems to make this better behaved in environments such as PyQt and gdb
+    dt = 1e-3
+    while dt < 1:
+        p = Popen(['otool', '-L', _rl.__file__], stdout=PIPE, stderr=PIPE)
+        otool,err = p.communicate()
+
+        if p.returncode == 4:
+            # EINTR
+            time.sleep(dt)
+            dt *= 2
+            continue
+        elif p.returncode:
+            warnings.warn("libedit detection failed: %s"%err)
+            break
+        else:
             break
-        except IOError, (errno, strerror):
-            if errno == 4:
-                continue
-            else:
-                break
 
-    if status == 0 and len(result) > 0:
+    if p.returncode == 0 and re.search(r'/libedit[\.\d+]*\.dylib\s', otool):
         # we are bound to libedit - new in Leopard
         _rl.parse_and_bind("bind ^I rl_complete")
         warnings.warn("Leopard libedit detected - readline will not be well behaved "
             "including some crashes on tab completion, and incorrect history navigation. "
             "It is highly recommended that you install readline, "
             "which is easy_installable with: 'easy_install readline'",
             RuntimeWarning)
         uses_libedit = True
 
 
 # the clear_history() function was only introduced in Python 2.4 and is
 # actually optional in the readline API, so we must explicitly check for its
 # existence.  Some known platforms actually don't have it.  This thread:
 # http://mail.python.org/pipermail/python-dev/2003-August/037845.html
 # has the original discussion.
 
 if have_readline:
     try:
         _rl.clear_history
     except AttributeError:
         def clear_history(): pass
         _rl.clear_history = clear_history