def create_unique_id(prefix, existing_ids):
if prefix in existing_ids:<EOL><INDENT>suffix = <NUM_LIT:1><EOL>while True:<EOL><INDENT>new_id = '<STR_LIT>'.format(prefix, suffix)<EOL>if new_id not in existing_ids:<EOL><INDENT>return new_id<EOL><DEDENT>suffix += <NUM_LIT:1><EOL><DEDENT><DEDENT>return prefix<EOL>
Return a unique string ID from the prefix.

    First check if the prefix is itself a unique ID in the set-like parameter
    existing_ids. If not, try integers in ascending order appended to the
    prefix until a unique ID is found.