django.template.base.VariableDoesNotExist: Failed lookup for key [script_url]

[copyNdpaste]

28/Jan/2024 05:55:15,013 base.py:_resolve_lookup:922 [DEBUG] Exception while resolving variable 'script_url' in template 'drf_spectacular/swagger_ui.html'.
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 875, in _resolve_lookup
    current = current[bit]
  File "/usr/local/lib/python3.9/site-packages/django/template/context.py", line 83, in __getitem__
    raise KeyError(key)
KeyError: 'script_url'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 881, in _resolve_lookup
    if isinstance(current, BaseContext) and getattr(
AttributeError: type object 'RequestContext' has no attribute 'script_url'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 891, in _resolve_lookup
    current = current[int(bit)]
ValueError: invalid literal for int() with base 10: 'script_url'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 898, in _resolve_lookup
    raise VariableDoesNotExist(
django.template.base.VariableDoesNotExist: Failed lookup for key [script_url] in [{'True': True, 'False': False, 'None': None}, {'csrf_token': <SimpleLazyObject: <function csrf.<locals>._get_val at 0xffff73cf5040>>, 'request': <rest_framework.request.Request: GET '/api/docs'>, 'user': <django.contrib.auth.models.AnonymousUser object at 0xffff73ce2e80>, 'perms': PermWrapper(<django.contrib.auth.models.AnonymousUser object at 0xffff73ce2e80>), 'messages': <FallbackStorage: request=<WSGIRequest: GET '/api/docs'>>, 'DEFAULT_MESSAGE_LEVELS': {'DEBUG': 10, 'INFO': 20, 'SUCCESS': 25, 'WARNING': 30, 'ERROR': 40}}, {}, {'title': 'API', 'swagger_ui_css': 'https://cdn.jsdelivr.net/npm/swagger-ui-dist@latest/swagger-ui.css', 'swagger_ui_bundle': 'https://cdn.jsdelivr.net/npm/swagger-ui-dist@latest/swagger-ui-bundle.js', 'swagger_ui_standalone': 'https://cdn.jsdelivr.net/npm/swagger-ui-dist@latest/swagger-ui-standalone-preset.js', 'favicon_href': 'https://cdn.jsdelivr.net/npm/swagger-ui-dist@latest/favicon-32x32.png', 'schema_url': '/api/schema', 'settings': '{\n  "deepLinking": true\n}', 'oauth2_config': '{}', 'template_name_js': 'drf_spectacular/swagger_ui.js', 'csrf_header_name': 'X-CSRFTOKEN', 'schema_auth_names': '[]'}, {'block': <Block Node: body. Contents: [<TextNode: '\n    <div id="swagger-ui"'>, <Variable Node: swagger_ui_bundle>, <TextNode: '"></script>\n    <script s'>, <Variable Node: swagger_ui_standalone>, <TextNode: '"></script>\n    '>, <IfNode>, <TextNode: '\n    '>]>}]

settings.py

INSTALLED_APPS = [
    "drf_spectacular",

]
REST_FRAMEWORK = {
    "DEFAULT_SCHEMA_CLASS": "drf_spectacular.openapi.AutoSchema",
}

urls.py

urlpatterns = [
    path(
        "api/schema",
        SpectacularAPIView.as_view(),
        name="schema",
    ),
    path(
        "api/docs",
        SpectacularSwaggerView.as_view(url_name="schema"),
        name="swagger-ui",
    ),
]

why VariableDoesNotExist error is raised?

[copyNdpaste]

SERVER_ENV=local ./manage.py spectacular --file schema.yaml --validate -> Schema generation summary: Warnings: 1 (1 unique) Errors: 0 (0 unique)

[tfranzel]

Hi, this is highly unusual. I'm not even sure how it is possible that line 22 produces an error. By definition the if is safe even if the variable is not existing, in which case false is assumed.

https://github.com/tfranzel/drf-spectacular/blob/a616766528b9a97516b03496354a56755762f914/drf_spectacular/templates/drf_spectacular/swagger_ui.html#L22-L27

• Are you sure nothing else is broken on your side, since this works flawlessly for a lot of people and we haven't changed anything here for quite a while.
• Do regular requests work for you?
• Which version of Django/DRF/spectacular are you using?

[BramEsposito]

@copyNdpaste do you have Django Debug Toolbar installed? I run into these errors when the Toolbar is visible.

[vcleal]

This is just a debug level log from the 'django' logger, it logs the exception but replaces the variable with context.template.engine.string_if_invalid, which is an empty string by default, so there are no errors in request or templates rendering. You can check the code in the file "/usr/local/lib/python3.9/site-packages/django/template/base.py" or https://github.com/django/django/blob/fa7848146738a9fe1d415ee4808664e54739eeb7/django/template/base.py#L931-L945 for example.

...
        except Exception as e:
            template_name = getattr(context, "template_name", None) or "unknown"
            logger.debug(
                "Exception while resolving variable '%s' in template '%s'.",
                bit,
                template_name,
                exc_info=True,
            )

            if getattr(e, "silent_variable_failure", False):
                current = context.template.engine.string_if_invalid
            else:
                raise

        return current

https://docs.djangoproject.com/en/5.0/ref/templates/api/#how-invalid-variables-are-handled

[tfranzel]

thx @vcleal this finally makes sense, I believe. Since there is no nice&short way of checking for existence, it is easier to just set this var to None in the main use-case.

I think this should fix it then. Feedback welcome.