Scott Gould wrote: > Hi folks, > > This is a head-scratcher to me. I occasionally get this error: > > --- > File "/var/www/myproj/account/views.py", line 54, in account > if request.account.is_instructor and request.account.contact and > request.account.contact.relationship.institution_party_number: > > AttributeError: 'NoneType' object has no attribute 'relationship' > --- > > I'm leaving out all the supporting code deliberately. My question is > simple: if python short-circuits evaluation and > "request.account.contact" is None, how is it even getting as far as > "request.account.contact.relationship.institution_party_number"?
Probably a race condition: contact is set to None after request.account.contact is evaluated, but before request.account.contact.relationship is evaluated. This may happen in your case because the underlying database was modified by a different user (I'm speculating). Here's a simulation: >>> class Contact: ... relationship = "SUCCESS" ... >>> class Account(object): ... def __init__(self): ... self._contact = Contact() ... @property ... def contact(self): ... try: return self._contact ... finally: self._contact = None ... >>> account = Account() >>> account.contact and account.contact.relationship Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'NoneType' object has no attribute 'relationship' You can avoid the problem with a different coding style: >>> account = Account() >>> try: ... print account.contact.relationship ... except AttributeError: ... print "failed" ... SUCCESS Peter -- http://mail.python.org/mailman/listinfo/python-list
