Inside the file calendar.py, there are two functions which are supposed to calculate the previous and next month relative to the actual year and month.

def _prevmonth(year, month):
    if month == 1:
        return year-1, 12
    else:
        return year, month-1


def _nextmonth(year, month):
    if month == 12:
        return year+1, 1
    else:
        return year, month+1

Because of the concise calculation that is being made by these functions, it would be convenient to use the ternary operator to calculate that. So, the result would be:

def _prevmonth(year, month):
    return [year-1, 12] if month == 1 else [year, month-1]

def _nextmonth(year, month):
    return [year+1, 1] if month == 12 else [year, month+1]

Why do you care what the implementation of the private methods are? Does it make them faster or fix a bug? How is it "convenient" to change the implementation to ternary if?

Without some better justification, this strikes me as just code churn for no benefit, but the risk of breaking things. For example, you changed the result from a tuple to a list.

Will this break anything? I don't know, but it will take time to find out, and with no obvious benefit to the change, spending that time to find out if this is a safe change is effort for no visible benefit.

I concur with Steven. We usually reject pure cosmetic changes. And I do not see any advantages of the new code.