skipping a function if returned value is None?

Question

Is there anyway to avoid a function call if function returns None? I'm doing this at the moment, but it seems very inefficient calling the function twice

if  bool(runChecks(problems)):
    return  runChecks(problems)

I would rather do this in one line of code, instead of calling it twice. If it returns True, then it returns a string with the error.

If it returns false, then it continues with the rest of the program. The runChecks() is a function that makes sure input is viable for program. no letters or chars that I havnt programmed it for

Answer 1

Try the walrus operator

if val:=runChecks(problems):
    return val

Answer 2

value = runChecks(problems)
if value:
    return value