def parse_file_string(filestring):
    """
    >>> parse_file_string("File 123: ABC (X, Y) Z")
    ('ABC (X, Y) Z', '')
    >>> parse_file_string("File 123: ABC (X) Y (Z)")
    ('ABC (X) Y', 'Z')
    >>> parse_file_string("File: ABC")
    ('ABC', '')
    >>> parse_file_string("File 2: A, B, 1-2")
    ('A, B, 1-2', '')
    """
    if filestring.strip()[-1] != ")":
        filestring=filestring.strip()+"()"
    if ':' in filestring:
        rhs = filestring.partition(":")[2]
    else:
        rhs = filestring
    chunks = rhs.split('(')
    indname = '('.join(chunks[:-1])
    units = chunks[-1].replace(')','')
    return indname.strip(), units.strip()