Question

In Perl, it’s often nice to be able to assign an object, but specify some fall-back value if the variable being assigned from is ‘undef’. For instance:

my $x = undef;
my $y = 2;
my $a = $x || $y;

After this,

$a == 2

Is there a concise way to achieve this in Python if the value x is None, or would a full-on …

if x is not None
    a = x
else
    a = y

… be the most Pythonic way to achieve this?

EDIT: Apologies, as has been pointed out by several commenters, I wasn’t really talking about the value being undefined, but ‘undef’ in Perl, which is not really the same thing. But the question as originally worded didn’t make this clear.

Answer 1

Since 2.5:

If you want to fall back only on None:

a = x if x is not None else y 

If you want to fall back also on empty string, false, 0 etc.:

a = x if x else y 

or

a = x or y 

---

As for undefined (as never defined, a.k.a. not bound):

try:
  a = x 
except NameError:
  a = y

or a bit more hackish (I’d not really recommend that, but it’s short):

a = vars().get('x',y)