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

@@ -9,9 +9,13 b' 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
@@ -44,24 +48,29 b" if sys.platform == 'win32' and have_readline:"
         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__ )
-            break
-        except IOError, (errno, strerror):
-            if errno == 4:
+    # 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
 
-    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 "