Error trying to modify data with python code in plone

Hi,
I am new to Plone.  I have some python code written to modify data and I am getting errors.
The line that produces the error is

    obj.setLast_name2()

The error is

  *   <PythonScript at /yc1/test2>
Line 38
  *   Module AccessControl.ImplPython, line 675, in guarded_getattr

AttributeError: setLast_name2



I have been googling this and I came across something that said you have to use an external method to have full permissions to run certain code.  Later I came across another posting that said external methods are obsolete and one should use views.  I am quite confused right now.  Can someone point me in the right direction and how I should go about doing it?

Full Python code:
from AccessControl import getSecurityManager
from StringIO import StringIO
from Products.CMFCore.utils import getToolByName
membership = getToolByName(context, 'portal_membership')
username = context.portal_membership.getAuthenticatedMember().getUserName()
print username
buf = StringIO()
itemp = context.portal_catalog.queryCatalog({
            "portal_type":("Staff","Faculty"),
            "path":"/yc1/portal_college/rnunez",
            "sort_on" : "created" })

items = list(itemp)
context.manage_setLocalRoles(username, ['Manager', 'Owner','Editor'])
#context.manage_permission('Edit', roles=['Manager', 'Owner','Editor'], acquire=True)
print >> buf, "Found %d items to be Updated" % len(items)
getSecurityManager().checkPermission('View', context)
roles2 = [r['name'] for r in context.rolesOfPermission('View') if r['selected']]
#context.portal.rolesOfPermission('Modify portal content')
count = 0
for b in items:
    count += 1
    obj = b.getObject()
    #obj.declareObjectPublic() # like __roles__ = ACCESS_PUBLIC
    #print >> buf, "updating:" + obj.absolute_url()
    #obj.at_post_edit_script
    m=obj.getLast_name()
    print m
    obj.setLast_name2()
    m=obj.getLast_name()
    print m


return buf.getvalue(), printed


Full Error:

We're sorry, but there seems to be an error...

Here is the full error message:

Display traceback as text<http://172.16.140.23:8080/yc1/error_log/getLogEntryAsText?id=1435073426.330.969255523092>

Traceback (innermost last):

  *   Module ZPublisher.Publish, line 138, in publish
  *   Module ZPublisher.mapply, line 77, in mapply
  *   Module ZPublisher.Publish, line 48, in call_object
  *   Module Shared.DC.Scripts.Bindings, line 322, in __call__
  *   Module Shared.DC.Scripts.Bindings, line 359, in _bindAndExec
  *   Module Products.PythonScripts.PythonScript, line 344, in _exec
  *   Module script, line 38, in test2
<PythonScript at /yc1/test2>
Line 38
  *   Module AccessControl.ImplPython, line 675, in guarded_getattr

AttributeError: setLast_name2

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