def __init__(self, download_dir=None):
        """
        `download_dir` - If `None` then downloaded files will be temporary files
        that are deleted on close. If set to a value, then downloaded files
        will be saved to this directory, and will not be automatically deleted.
        """
        self._delete_on_close = download_dir is None
        self.download_dir = download_dir

        `download_dir` - If `None` then downloaded files will be temporary files
        that are deleted on close. If set to a value, then downloaded files
        will be saved to this directory, and will not be automatically deleted.
        
apistar/client/decoders.py