PyPI simple API returns 500 when BrowsableAPIRenderer is selected (no template_name set)

[dkliban]

Summary

The PyPI simple index view returns HTTP 500 when DRF's BrowsableAPIRenderer is selected during content negotiation. This happens when clients request /api/pypi/<domain>/<path>/simple/<package>/ without ?format=json — the view returns a TemplateResponse without setting template_name, causing BrowsableAPIRenderer.get_template_names() to raise ImproperlyConfigured.

Requests to the same endpoints with ?format=json succeed (HTTP 200).

Error

django.core.exceptions.ImproperlyConfigured: Returned a template response with no `template_name` attribute set on either the view or response

Full traceback

File "django/core/handlers/base.py", line 220, in _get_response
    response = response.render()
File "django/template/response.py", line 114, in render
    self.content = self.rendered_content
File "rest_framework/response.py", line 74, in rendered_content
    ret = renderer.render(self.data, accepted_media_type, context)
File "rest_framework/renderers.py", line 156, in render
    template_names = self.get_template_names(response, view)
File "rest_framework/renderers.py", line 188, in get_template_names
    raise ImproperlyConfigured(
django.core.exceptions.ImproperlyConfigured: Returned a template response with no `template_name` attribute set on either the view or response

Reproduction

Requests without ?format=json fail:

GET /api/pypi/<domain>/<path>/simple/<package>/ → 500

Requests with ?format=json succeed:

GET /api/pypi/<domain>/<path>/simple/<package>/?format=json → 200

Impact observed in production

• 76 occurrences across 22 of 50 API pods in a ~30-minute window (2026-07-24)
• A previous burst of 962 errors in ~35 minutes (2026-07-23) may have the same root cause
• Affected clients: uv (pip install subcommand does not append ?format=json; pip compile does), curl
• All affected URLs follow the pattern: /api/pypi/public-rhai/rhoai/3.5/{variant}/simple/{package}/

Expected behavior

The simple index view should either:

1. Set a template_name on the response so the BrowsableAPIRenderer can render it, or
2. Exclude BrowsableAPIRenderer from the view's renderer_classes, or
3. Handle content negotiation so that non-JSON requests get a valid HTML or application/vnd.pypi.simple.v1+html response

Environment

• pulp_python deployed on pulp-service (packages.redhat.com)
• Django REST Framework BrowsableAPIRenderer is in the default renderer classes