Detecting cpus/cores in Python

I found this interesting function in a post on Twister and distributed programming by Bruce Eckel. It uses the Python os package to detect the number of CPUs/cores on a machine. Archiving it here for future reference

def detectCPUs():
 """
 Detects the number of CPUs on a system. Cribbed from pp.
 """
 # Linux, Unix and MacOS:
 if hasattr(os, "sysconf"):
     if os.sysconf_names.has_key("SC_NPROCESSORS_ONLN"):
         # Linux & Unix:
         ncpus = os.sysconf("SC_NPROCESSORS_ONLN")
         if isinstance(ncpus, int) and ncpus > 0:
             return ncpus
     else: # OSX:
         return int(os.popen2("sysctl -n hw.ncpu")[1].read())
 # Windows:
 if os.environ.has_key("NUMBER_OF_PROCESSORS"):
         ncpus = int(os.environ["NUMBER_OF_PROCESSORS"]);
         if ncpus > 0:
             return ncpus
 return 1 # Default