Hi, I am running the same code on Ubuntu 10.04 and MacOS 10.7 with different results. On Ubuntu, it reads a dataset from a .mat Matlab file, and then tries to access specific values. On MacOS I get: Done loading matlab data. Traceback (most recent call last): File "parse_proximity.py", line 79, in <module> get_events(matlab_obj) File "parse_proximity.py", line 18, in get_events subject_mac = int(subject_object.my_mac[0][0][0], 16) AttributeError: 'numpy.void' object has no attribute 'my_mac' The code looks like this: import scipy.io from datetime import datetime, timedelta import time import sys, os start_date = 1095984000 end_date = 1096004000 def get_events(matlab_obj): subjects = matlab_obj["s"][0] for subject_object in subjects: valid = True try: subject_mac = int(subject_object.my_mac[0][0][0], 16) ... if __name__ == "__main__": matlab_filename = sys.argv[1] matlab_obj = scipy.io.loadmat(matlab_filename) print "Done loading matlab data." get_events(matlab_obj) I have tried two different versions of python 2.6.1 and 2.7.1 with same results. I don't have any other problems with using python on MacOS. Any suggestions? Regards, Håkan