Use dataclass to initialize default values

import abc

from dataclasses import dataclass, field

import os

import time

from typing import (

    browsable: NotRequired[bool]

@dataclass

class FilesSourceOptions:

    """Options to control behavior of file source operations, such as realize_to, write_from and list."""

    # the HTTPFilesSource passes in additional http_headers through these properties, which

    # are merged with constructor defined http_headers. The interpretation of these properties

    # are filesystem specific.

    extra_props: Optional[FilesSourceProperties] = {}

    extra_props: Optional[FilesSourceProperties] = field(default_factory=lambda: {})

class SingleFileSource(metaclass=abc.ABCMeta):