'Normalize and convert all keys to BlobKey type.
This method is based on datastore.NormalizeAndTypeCheck().
Args:
keys: A single key or a list/tuple of keys.  Keys may be a string
or BlobKey
Returns:
Single key or list with all strings replaced by BlobKey instances.'

@classmethod
def __normalize_and_convert_keys(cls, keys):

    if isinstance(keys, (list, tuple)):
        multiple = True
        keys = list(keys)
    else:
        multiple = False
        keys = [keys]
    for (index, key) in enumerate(keys):
        if (not isinstance(key, (basestring, BlobKey))):
            raise datastore_errors.BadArgumentError(('Expected    str    or    BlobKey;    received    %s    (a    %s)' % (key, datastore.typename(key))))
        keys[index] = datastore.Key.from_path(cls.kind(), str(key), namespace='')
    if multiple:
        return keys
    else:
        return keys[0]
