R – openid attribute exchange

An OpenID identifier can technically be as long as a legal URL can be (practically around 2K), but I'd say 150 characters is a good maximum.

Incidentally be sure to store the Claimed Identifier as the primary key (or equivalent lookup column) rather than the user-supplied identifier or any other variation that you might see in the authentication process. Also, to really be secure, you need to do a case sensitive comparison on the path of the URL (you can be case insensitive in the host area). Since the case sensitivity issue is complicated, I just always normalize the host to lowercase, and then do a case sensitive compare on the whole string.

Try hasattr():

if hasattr(a, 'property'):
    a.property

See zweiterlinde's answer below, who offers good advice about asking forgiveness! A very pythonic approach!

The general practice in python is that, if the property is likely to be there most of the time, simply call it and either let the exception propagate, or trap it with a try/except block. This will likely be faster than hasattr. If the property is likely to not be there most of the time, or you're not sure, using hasattr will probably be faster than repeatedly falling into an exception block.