Serialize Custom Python Objects to JSON-Friendly Dictionaries

from dataclasses import asdict, is_dataclass
from datetime import datetime, date
from typing import Any

def serialize_object_to_dict(obj: Any) -> Any:
    """ Recursively converts an object (especially dataclasses) into a JSON-serializable dictionary. """
    if is_dataclass(obj):
        # Convert dataclass to dict
        data = asdict(obj)
        return {k: serialize_object_to_dict(v) for k, v in data.items()}
    elif isinstance(obj, (datetime, date)):
        # Convert datetime/date objects to ISO 8601 string
        return obj.isoformat()
    elif isinstance(obj, dict):
        # Recursively process dictionary values
        return {k: serialize_object_to_dict(v) for k, v in obj.items()}
    elif isinstance(obj, list):
        # Recursively process list items
        return [serialize_object_to_dict(item) for item in obj]
    else:
        # Return primitive types as is
        return obj

# --- Example Usage with Dataclass (from previous snippet) ---
from dataclasses import dataclass, field
from typing import List, Optional

@dataclass
class UserProfile:
    username: str
    email: str
    age: Optional[int] = None
    created_at: datetime = field(default_factory=datetime.now)
    roles: List[str] = field(default_factory=list)

@dataclass
class APIResponse:
    status_code: int
    message: str
    data: Optional[UserProfile] = None

user_profile = UserProfile("coder_guy", "[email protected]", age=35, roles=["developer"])
api_response_obj = APIResponse(200, "Profile data retrieved", user_profile)

# Convert to JSON-friendly dictionary
json_friendly_dict = serialize_object_to_dict(api_response_obj)

import json
print(json.dumps(json_friendly_dict, indent=2))

# Output will be a valid JSON string, with datetime converted:
# {
#   "status_code": 200,
#   "message": "Profile data retrieved",
#   "data": {
#     "username": "coder_guy",
#     "email": "[email protected]",
#     "age": 35,
#     "created_at": "2023-10-27T10:30:00.123456", (example date/time)
#     "roles": [
#       "developer"
#     ]
#   }
# }