diff --git a/core/roslib/src/roslib/genpy.py b/core/roslib/src/roslib/genpy.py
index 4131267d..62f157d1 100644
--- a/core/roslib/src/roslib/genpy.py
+++ b/core/roslib/src/roslib/genpy.py
@@ -884,8 +884,8 @@ def serialize_fn_generator(package, spec, is_numpy=False):
     for y in serializer_generator(package, flatten(spec), True, is_numpy):
         yield "  "+y 
     pop_context()
-    yield "except struct.error, se: self._check_types(se)"
-    yield "except TypeError, te: self._check_types(te)" 
+    yield "except struct.error as se: self._check_types(se)"
+    yield "except TypeError as te: self._check_types(te)" 
     # done w/ method-var context #
     
 def deserialize_fn_generator(package, spec, is_numpy=False):
@@ -919,7 +919,7 @@ def deserialize_fn_generator(package, spec, is_numpy=False):
             yield "  %s"%code
     
     yield "  return self"
-    yield "except struct.error, e:"
+    yield "except struct.error as e:"
     yield "  raise roslib.message.DeserializationError(e) #most likely buffer underfill"
 
 def msg_generator(package, name, spec):
@@ -943,7 +943,7 @@ def msg_generator(package, name, spec):
     # for older versions of msg files
     try:
         gendeps_dict = roslib.gentools.get_dependencies(spec, package, compute_files=False)
-    except roslib.msgs.MsgSpecException, e:
+    except roslib.msgs.MsgSpecException as e:
         raise MsgGenerationException("Cannot generate .msg for %s/%s: %s"%(package, name, str(e)))
     md5sum = roslib.gentools.compute_md5(gendeps_dict)
     
diff --git a/tools/rosmake/src/rosmake/parallel_build.py b/tools/rosmake/src/rosmake/parallel_build.py
index f002cbd3..72da5478 100644
--- a/tools/rosmake/src/rosmake/parallel_build.py
+++ b/tools/rosmake/src/rosmake/parallel_build.py
@@ -40,6 +40,19 @@ import roslib
 import roslib.rospack
 import threading
 
+if sys.hexversion > 0x03000000: #Python3
+    python3 = True
+else:
+    python3 = False
+
+def _read_stdout(cmd):
+    p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    std_out, std_err = p.communicate()
+    if python3:
+        return std_out.decode()
+    else:
+        return std_out    
+
 def num_cpus():
   """
   Detects the number of CPUs on a system. Cribbed from pp.
@@ -52,7 +65,7 @@ def num_cpus():
       if isinstance(ncpus, int) and ncpus > 0:
         return ncpus
     else: # OSX:
-      return subprocess.call("sysctl -n hw.ncpu".split())
+      return int(_read_stdout(["sysctl", "-n", "hw.ncpu"])) or 1
   # Windows:
   if "NUMBER_OF_PROCESSORS" in os.environ:
     ncpus = int(os.environ["NUMBER_OF_PROCESSORS"]);