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

$a == 2

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

a = x if x is not None else y

a = x if x else y

a = x or y

try:
  a = x
except NameError:
  a = y

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

a = y if x is None else x

try:
    a = x
except:
    a = y

my $x = undef;

my $x;

my $a = $x || $y;

my $a = $x // $y;

def myRange(start, stop=None):
    start, stop = (0, start) if stop is None else (start, stop)
    ...

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

a = x if x is not None else y

>>> x = 0
>>> y = 2
>>> a = x or y
>>> a
2
>>>

if 'x' in dir():
    a = x
except:
     a =y

try:
    a = x
else:
    a = y

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

x = myfunction()

if x is None:
    x = y

print x

try:
    x = myfunction()
except AnException:
    x = "fallback"

print x

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

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

def MyFunc( a=2 ):
    print "a is %d"%a

>>> MyFunc()
...a is 2
>>> MyFunc(5)
...a is 5