human
Complete the below
def index_db(index_filename, filenames=None, format=None, key_function=None, **kwargs):

    ''''Indexes several search output files into an SQLite database.
    - index_filename - The SQLite filename.
    - filenames    - List of strings specifying file(s) to be indexed, or when
    indexing a single file this can be given as a string.
    (optional if reloading an existing index, but must match)
    - format       - Lower case string denoting one of the supported formats.
    (optional if reloading an existing index, but must match)
    - key_function - Optional callback function which when given a
    QueryResult identifier string should return a unique
    key for the dictionary.
    - kwargs       - Format-specific keyword arguments.
    The `index_db` function is similar to `index` in that it indexes the start
    position of all queries from search output files. The main difference is
    instead of storing these indices in-memory, they are written to disk as an
    SQLite database file. This allows the indices to persist between Python
    sessions. This enables access to any queries in the file without any
    indexing overhead, provided it has been indexed at least once.
    >>> from Bio import SearchIO
    >>> idx_filename = ":memory:" # Use a real filename, this is in RAM only!
    >>> db_idx = SearchIO.index_db(idx_filename, \'Blast/mirna.xml\', \'blast-xml\')
    >>> sorted(db_idx)
    [\'33211\', \'33212\', \'33213\']
    >>> db_idx[\'33212\']
    QueryResult(id=\'33212\', 44 hits)
    >>> db_idx.close()
    `index_db` can also index multiple files and store them in the same
    database, making it easier to group multiple search files and access them
    from a single interface.
    >>> from Bio import SearchIO
    >>> idx_filename = ":memory:" # Use a real filename, this is in RAM only!
    >>> files = [\'Blast/mirna.xml\', \'Blast/wnts.xml\']
    >>> db_idx = SearchIO.index_db(idx_filename, files, \'blast-xml\')
    >>> sorted(db_idx)
    [\'33211\', \'33212\', \'33213\', \'gi|156630997:105-1160\', ..., \'gi|53729353:216-1313\']
    >>> db_idx[\'33212\']
    QueryResult(id=\'33212\',...'''
assistant
#Here is the Python code you requested.
    if isinstance(filenames, basestring):
        filenames = [filenames]
    from Bio.File import _SQLiteManySeqFilesDict
    repr = ('SearchIO.index_db(%r,    filenames=%r,    format=%r,    key_function=%r,    ...)' % (index_filename, filenames, format, key_function))
    def proxy_factory(format, filename=None):
        'Given    a    filename    returns    proxy    object,    else    boolean    if    format    OK.'
        if filename:
            return get_processor(format, _INDEXER_MAP)(filename, **kwargs)
        else:
            return (format in _INDEXER_MAP)
    return _SQLiteManySeqFilesDict(index_filename, filenames, proxy_factory, format, key_function, repr)