diff -r 6f4627a65c0a Doc/library/os.rst
--- a/Doc/library/os.rst	Sun May 05 08:14:53 2013 +0200
+++ b/Doc/library/os.rst	Sat May 11 07:32:48 2013 -0400
@@ -3155,9 +3155,10 @@
    Return the set of CPUs the process with PID *pid* (or the current process
    if zero) is restricted to.
 
-   .. seealso::
-      :func:`multiprocessing.cpu_count` returns the number of CPUs in the
-      system.
+
+.. function:: cpu_count()
+
+   Return the number of CPUs in the system. Returns None if undetermined.
 
 
 .. _os-path:
diff -r 6f4627a65c0a Lib/multiprocessing/__init__.py
--- a/Lib/multiprocessing/__init__.py	Sun May 05 08:14:53 2013 +0200
+++ b/Lib/multiprocessing/__init__.py	Sat May 11 07:32:48 2013 -0400
@@ -85,30 +85,11 @@
     '''
     Returns the number of CPUs in the system
     '''
-    if sys.platform == 'win32':
-        try:
-            num = int(os.environ['NUMBER_OF_PROCESSORS'])
-        except (ValueError, KeyError):
-            num = 0
-    elif 'bsd' in sys.platform or sys.platform == 'darwin':
-        comm = '/sbin/sysctl -n hw.ncpu'
-        if sys.platform == 'darwin':
-            comm = '/usr' + comm
-        try:
-            with os.popen(comm) as p:
-                num = int(p.read())
-        except ValueError:
-            num = 0
+    num = os.cpu_count()
+    if num == None:
+        raise NotImplementedError('cannot determine number of cpus')
     else:
-        try:
-            num = os.sysconf('SC_NPROCESSORS_ONLN')
-        except (ValueError, OSError, AttributeError):
-            num = 0
-
-    if num >= 1:
         return num
-    else:
-        raise NotImplementedError('cannot determine number of cpus')
 
 def freeze_support():
     '''
diff -r 6f4627a65c0a Lib/os.py
--- a/Lib/os.py	Sun May 05 08:14:53 2013 +0200
+++ b/Lib/os.py	Sat May 11 07:32:48 2013 -0400
@@ -32,7 +32,7 @@
 __all__ = ["altsep", "curdir", "pardir", "sep", "pathsep", "linesep",
            "defpath", "name", "path", "devnull", "SEEK_SET", "SEEK_CUR",
            "SEEK_END", "fsencode", "fsdecode", "get_exec_path", "fdopen",
-           "popen", "extsep"]
+           "popen", "extsep", "cpu_count"]
 
 def _exists(name):
     return name in globals()
@@ -1016,3 +1016,31 @@
         raise TypeError("invalid fd type (%s, expected integer)" % type(fd))
     import io
     return io.open(fd, *args, **kwargs)
+
+def cpu_count():
+    '''
+    Returns the number of CPUs in the system
+    '''
+    if sys.platform == 'win32':
+        try:
+            num = int(environ['NUMBER_OF_PROCESSORS'])
+        except (ValueError, KeyError):
+            num = None
+    elif 'bsd' in sys.platform or sys.platform == 'darwin':
+        comm = '/sbin/sysctl -n hw.ncpu'
+        if sys.platform == 'darwin':
+            comm = '/usr/sbin/sysctl -n hw.activecpu'
+        else:
+            comm = '/sbin/sysctl -n hw.ncpu'
+        try:
+            with popen(comm) as p:
+                num = int(p.read())
+        except ValueError:
+            num = None
+    else:
+        try:
+            num = sysconf('SC_NPROCESSORS_ONLN')
+        except (ValueError, OSError, AttributeError):
+            num = None
+
+    return num
diff -r 6f4627a65c0a Lib/test/test_os.py
--- a/Lib/test/test_os.py	Sun May 05 08:14:53 2013 +0200
+++ b/Lib/test/test_os.py	Sat May 11 07:32:48 2013 -0400
@@ -2216,6 +2216,13 @@
                 else:
                     self.fail("No exception thrown by {}".format(func))
 
+class CPUCountTests(unittest.TestCase):
+    def test_cpu_count(self):
+        cpus = os.cpu_count()
+        self.assertTrue((type(cpus) is int) or (cpus is None))
+        self.assertTrue(cpus != 0)
+        self.assertTrue(cpus >= 1 or cpus == None)
+
 @support.reap_threads
 def test_main():
     support.run_unittest(
@@ -2246,6 +2253,7 @@
         TermsizeTests,
         OSErrorTests,
         RemoveDirsTests,
+        CPUCountTests,
     )
 
 if __name__ == "__main__":
diff -r 6f4627a65c0a Misc/NEWS
--- a/Misc/NEWS	Sun May 05 08:14:53 2013 +0200
+++ b/Misc/NEWS	Sat May 11 07:32:48 2013 -0400
@@ -69,6 +69,8 @@
 Library
 -------
 
+- Issue #17914: Add os.cpu_count()
+
 - Issue #14173: Avoid crashing when reading a signal handler during
   interpreter shutdown.