pylab.xlim(0.5,6.5) should be:
pylab.xlim(min_x-(bar_width/2),max_x+(bar_width/2)) -- http://mail.python.org/mailman/listinfo/python-list
pylab.xlim(0.5,6.5) should be:
pylab.xlim(min_x-(bar_width/2),max_x+(bar_width/2)) -- http://mail.python.org/mailman/listinfo/python-list