Agfdhyk

I have this:

try:    

    if session.var:

        otherVar = session.var

    else:

        util = db.utility[1]

        otherVar = session.var = util.freshOutTheBank

except AttributeError:

    util = db.utility[1]

    otherVar = session.var = util.freshOutTheBank



...do stuff with otherVar

The case is that the session.var might not exist or could be None. This code is also run more than once by a user during a session.

How do I avoid repeating the code. I basically want to do an 'except and else' or am I looking at this incorrectly?

Assuming this is a web2py session object, note that it is an instance of gluon.Storage, which is like a dictionary with two exceptions: (1) keys can be accessed like properties, and (2) accessing a non-existent key/property returns None rather than raising an exception. So, you can simply do something like:

otherVar = session.var = session.var if session.var else db.utility[1].freshOutTheBank

Note, if you want to distinguish between non-existent keys and keys that have an explicit value of None, you cannot use hasattr(session, 'var'), as that will return True even if there is no 'var' key. Instead, you can check session.has_key('var'), which will return False if there is no 'var' key.

You can avoid using session.var if it doesn't exist by checking for it first, using hasattr. This avoids the need for the try/except block all together.

if hasattr(session, 'var') and session.var is not None:

    ...

else:

    ...

An alternative might be to have the else in your original code just raise an exception to get to the except block, but it's sort of ugly:

try:

    if session.var:

        ...

    else:

        raise AttributeError

except AttributeError:

    ...

In this situation, I think the "Look Before you Leap" style of programming (using hasattr) is nicer than the usually more Pythonic style of "Easier to Ask Forgiveness than Permission" (which uses exceptions as part of flow control). But either one can work.

If your code was compartmentalized into smaller functions, it might be even easier to deal with the issue. For instance, if you wrote a get_session_var function, it could return from the successful case (inside the try and if blocks), and the two error cases could be resolved later:

def get_session_var(session):

    try:

        if session.var:

            return session.var

    except AttributeError:

        pass



    util = db.utility[1]

    session.var = util.freshOutTheBank

    return session.var