Django-Styleguide/utils.py

from rest_framework import serializers
from rest_framework import exceptions as rest_exceptions

from django.core.exceptions import ValidationError


def create_serializer_class(name, fields):
    return type(name, (serializers.Serializer, ), fields)


def inline_serializer(*, fields, data=None, **kwargs):
    serializer_class = create_serializer_class(name='', fields=fields)

    if data is not None:
        return serializer_class(data=data, **kwargs)

    return serializer_class(**kwargs)


def get_first_matching_attr(obj, *attrs, default=None):
    for attr in attrs:
        if hasattr(obj, attr):
            return getattr(obj, attr)

    return default


def get_error_message(exc):
    if hasattr(exc, 'message_dict'):
        return exc.message_dict
    error_msg = get_first_matching_attr(exc, 'message', 'messages')

    if isinstance(error_msg, list):
        error_msg = ', '.join(error_msg)

    if error_msg is None:
        error_msg = str(exc)

    return error_msg


class ExceptionHandlerMixin:
    """
    Mixin that transforms Django and Python exceptions into rest_framework ones.
    without the mixin, they return 500 status code which is not desired.
    """
    expected_exceptions = {
        ValueError: rest_exceptions.ValidationError,
        ValidationError: rest_exceptions.ValidationError,
        PermissionError: rest_exceptions.PermissionDenied
    }

    def handle_exception(self, exc):
        if isinstance(exc, tuple(self.expected_exceptions.keys())):
            drf_exception_class = self.expected_exceptions[exc.__class__]
            drf_exception = drf_exception_class(get_error_message(exc))

            return super().handle_exception(drf_exception)

        return super().handle_exception(exc)