def METHOD_NAME(self, data_key=None):
    za = self.dataset
    if data_key:
        za = za[data_key]
    else:
        data_key = ""
    path = os.path.join(self.source, data_key)
    if self.source.startswith("s3:"):
        path = path.replace("\\", "/")
        ld = ["s3://" + p for p in self.s3.ls(path)]
    else:
        path = path.replace("/", os.sep)
        ld = [os.path.join(path, p) for p in os.listdir(path)]
    return ld