import six


def list_as_string(option):
    """Returns the argument as a string.
    
    Useful for insuring that ConfigObj options are always returned
    as a string, despite the presence of a comma in the middle.
    
    Example:
    >>> print(list_as_string('a string'))
    a string
    >>> print(list_as_string(['a', 'string']))
    a, string
    >>> print(list_as_string('Reno, NV'))
    Reno, NV
    """
    # Check if it's already a string.
    if option is not None and not isinstance(option, six.string_types):
        return ', '.join(option)
    return option