Python: Assign Value if None Exists

Solution 1:

You should initialize variables to None and then check it:

var1 = None
if var1 is None:
    var1 = 4

Which can be written in one line as:

var1 = 4 if var1 is None else var1

or using shortcut (but checking against None is recommended)

var1 = var1 or 4

alternatively if you will not have anything assigned to variable that variable name doesn't exist and hence using that later will raise NameError, and you can also use that knowledge to do something like this

try:
    var1
except NameError:
    var1 = 4

but I would advise against that.

Solution 2:

var1 = var1 or 4

The only issue this might have is that if var1 is a falsey value, like False or 0 or [], it will choose 4 instead. That might be an issue.