[Python] Pythonic way to append function output to existing lists?

I have two functions that each return a tuple of lists. What is the most pythonic way to merge them? I am using tmp vars at the moment, which I find a bit awkward. Is there maybe a one-line-solution?

Here is my existing code, reduced to the bare minimum:

def check_this() -> Tuple[List[str], List[str]]:
problems = []
warnings = []
# do some tests to fill those lists with various error messages
return problems, warnings

def check_that() -> Tuple[List[str], List[str]]:
problems = []
warnings = []
# do some more tests to fill those lists with various error messages
return problems, warnings

def log_check_results(problems: List[str], warnings: List[str]):
logging.error("\n".join(problems))
logging.warning("\n".join(warnings))


I do not want to merge the check methods because they check completely different aspects of the project.

This was my first approach:

problems, warnings = check_this()
p, w = check_that()
problems.extend(p)
warnings.extend(w)
log_check_results(problems, warnings)


I have tried the following but find it harder to read (hence the question for a "pythonic" solution.)

problems, warnings = zip(check_this(), check_that())
log_check_results([m for l in problems for m in l],
[m for l in warnings for m in l])


Any better ideas?

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