What is the Pythonic way to use a default value when function returns None or throws exception?

Question

What's a more pythonic way of doing this?

try:
    a = foo() or b
except AttributeError:
    a = b

I want to set a to be the return of the function foo, but if foo returns None or an AttributeError exception is raised, then I want a to be set to b.

Answer 1

as pointed out by Gennady Kandaurov: you'd need to test for 'valid' return values of foo() that are not 'truthy' (as 0, [], (), ...):

try:
    a = foo() if foo() is not None else b
except AttributeError:
    a = b

depending on the implementation details of foo (whether it is expensive or has side-effects) you may want to call it once only:

try:
    f = foo()
    a = f if f is not None else b
except AttributeError:
    a = b