Proper use of the * operator in a oneline if statement python

Question

I'd like to know if its possible to use the * operator in a oneline if to achieve the following functionality:

if node['args'] != None:
    return_val = funct(*node['args'])
else:
    return_val = funct()

I thought I could just say

return_val = funct(*node['args'] if node['args'] != None else None)

but it turns out this is the same as saying

if node['args'] != None:
    return_val = funct(*node['args'])
else:
    return_val = funct(*None)

which doesn't make any sense for *None.

I tired enclosing the first option in parenthesis but this just throws SyntaxError: can't use starred expression here

return_val = funct((*node['args']) if node['args'] != None else None)

Answer 1

Yes, you need to provide an empty sequence, not None:

>>> def f(*args):
...     for arg in args:
...         print(arg)
...
>>> x = None
>>> y = ('a','b')
>>> f(*(y if x is not None else ()))
>>> x = object()
>>> f(*(y if x is not None else ()))
a
b

But I think your if -else statement approach is much preferable. I only have to look at it once and I know immediately what is going on. With the conditional expression, I have to think about it.

Also, this is a conditional expression, not a "one-line if statement".

Answer 2

A more concise solution, albeit one with slightly different semantics:

return_val = funct(*node['args'] or ())

If bool(node['args']) evaluates to False, the empty tuple () will be unpacked (into nothing) and passed; otherwise, node['args'] will be unpacked and passed.