How to find out the number of CPUs using python

If you have python with a version >= 2.6 you can simply use

import multiprocessingmultiprocessing.cpu_count()

http://docs.python.org/library/multiprocessing.html#multiprocessing.cpu_count

If you're interested into the number of processors available to your current process, you have to check cpuset first. Otherwise (or if cpuset is not in use), multiprocessing.cpu_count() is the way to go in Python 2.6 and newer. The following method falls back to a couple of alternative methods in older versions of Python:

import osimport reimport subprocessdef available_cpu_count():    """ Number of available virtual or physical CPUs on this system, i.e.    user/real as output by time(1) when called with an optimally scaling    userspace-only program"""    # cpuset    # cpuset may restrict the number of *available* processors    try:        m = re.search(r'(?m)^Cpus_allowed:\s*(.*)$',                      open('/proc/self/status').read())        if m:            res = bin(int(m.group(1).replace(',', ''), 16)).count('1')            if res > 0:                return res    except IOError:        pass    # Python 2.6+    try:        import multiprocessing        return multiprocessing.cpu_count()    except (ImportError, NotImplementedError):        pass    # https://github.com/giampaolo/psutil    try:        import psutil        return psutil.cpu_count()   # psutil.NUM_CPUS on old versions    except (ImportError, AttributeError):        pass    # POSIX    try:        res = int(os.sysconf('SC_NPROCESSORS_ONLN'))        if res > 0:            return res    except (AttributeError, ValueError):        pass    # Windows    try:        res = int(os.environ['NUMBER_OF_PROCESSORS'])        if res > 0:            return res    except (KeyError, ValueError):        pass    # jython    try:        from java.lang import Runtime        runtime = Runtime.getRuntime()        res = runtime.availableProcessors()        if res > 0:            return res    except ImportError:        pass    # BSD    try:        sysctl = subprocess.Popen(['sysctl', '-n', 'hw.ncpu'],                                  stdout=subprocess.PIPE)        scStdout = sysctl.communicate()[0]        res = int(scStdout)        if res > 0:            return res    except (OSError, ValueError):        pass    # Linux    try:        res = open('/proc/cpuinfo').read().count('processor\t:')        if res > 0:            return res    except IOError:        pass    # Solaris    try:        pseudoDevices = os.listdir('/devices/pseudo/')        res = 0        for pd in pseudoDevices:            if re.match(r'^cpuid@[0-9]+$', pd):                res += 1        if res > 0:            return res    except OSError:        pass    # Other UNIXes (heuristic)    try:        try:            dmesg = open('/var/run/dmesg.boot').read()        except IOError:            dmesgProcess = subprocess.Popen(['dmesg'], stdout=subprocess.PIPE)            dmesg = dmesgProcess.communicate()[0]        res = 0        while '\ncpu' + str(res) + ':' in dmesg:            res += 1        if res > 0:            return res    except OSError:        pass    raise Exception('Can not determine number of CPUs on this system')

Another option is to use the psutil library, which always turn out useful in these situations:

>>> import psutil>>> psutil.cpu_count()2

This should work on any platform supported by psutil(Unix and Windows).

Note that in some occasions multiprocessing.cpu_count may raise a NotImplementedError while psutil will be able to obtain the number of CPUs. This is simply because psutil first tries to use the same techniques used by multiprocessing and, if those fail, it also uses other techniques.