human
I wrote the below code

    fixture_count = 0
    loaded_object_count = 0
    fixture_object_count = 0
    tables = set()
    class SingleZipReader(zipfile.ZipFile, ):
        def __init__(self, *args, **kwargs):
            zipfile.ZipFile.__init__(self, *args, **kwargs)
            if settings.DEBUG:
                assert (len(self.namelist()) == 1), 'Zip-compressed    fixtures    must    contain    only    one    file.'
        def read(self):
            return zipfile.ZipFile.read(self, self.namelist()[0])
    compression_types = {None: file, 'gz': gzip.GzipFile, 'zip': SingleZipReader}
    if has_bz2:
        compression_types['bz2'] = bz2.BZ2File
    app_module_paths = []
    for app in get_apps():
        if hasattr(app, '__path__'):
            for path in app.__path__:
                app_module_paths.append(path)
        else:
            app_module_paths.append(app.__file__)
    app_fixtures = [os.path.join(os.path.dirname(path), 'fixtures') for path in app_module_paths]
    for fixture_label in fixture_labels:
        parts = fixture_label.split('.')
        if ((len(parts) > 1) and (parts[(-1)] in compression_types)):
            compression_formats = [parts[(-1)]]
            parts = parts[:(-1)]
        else:
            compression_formats = list(compression_types.keys())
        if (len(parts) == 1):
            fixture_name = parts[0]
            formats = serializers.get_public_serializer_formats()
        else:
            (fixture_name, format) = ('.'.join(parts[:(-1)]), parts[(-1)])
            if (format in serializers.get_public_serializer_formats()):
                formats = [format]
            else:
                formats = []
        if (not formats):
            return set()
        if os.path.isabs(fixture_name):
            fixture_dirs = [fixture_name]
        else:
            fixture_dirs = ((app_fixtures + list(settings.FIXTURE_DIRS)) + [''])
        for fixture_dir in fixture_dirs:
            label_found = False
            for combo in product([using, None], formats, compression_formats):
  ...

What's a good function header?

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

def tables_used_by_fixtures(fixture_labels, using=DEFAULT_DB_ALIAS):