Combine to argument into a single flat list

    It is used when you are not sure whether arguments are lists but want to combine them into one flat list

    Args:
        a1: list or other thing
        a2: list or other thing

    Returns:
        list: a flat list contain a1 and a2

def combine(a1, a2):
    ''' Combine to argument into a single flat list

    It is used when you are not sure whether arguments are lists but want to combine them into one flat list

    Args:
        a1: list or other thing
        a2: list or other thing

    Returns:
        list: a flat list contain a1 and a2
    '''
    if not isinstance(a1, list):
        a1 = [a1]
    if not isinstance(a2, list):
        a2 = [a2]
    return a1 + a2