human
Here's a good function header given the following:
I wrote the below code

    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)

What's a good function header?
assistant
#Here's a good function header.

def index_db(index_filename, filenames=None, format=None, key_function=None, **kwargs):