def split_extension(filename):
    """
	Splits the extension off the filename and returns a tuple of the
	base filename and the extension (without the dot).
	
	:param str filename: The base filename string to split.
	:return: A tuple of the head (characters before the last '.') and
			 the extension (characters after the last '.').
	"""
    parts = filename.split('.')
    if len(parts) < 2:
        return parts[0], ''
    ext = parts.pop(-1)
    head = '.'.join(parts)
    return head, ext
