Opened 8 years ago
Closed 8 years ago
#27359 closed New feature (fixed)
Make it possible to specify a default template engine
Reported by: | Artur Barseghyan | Owned by: | Carlton Gibson |
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Component: | Template system | Version: | 1.8 |
Severity: | Normal | Keywords: | template engines |
Cc: | Triage Stage: | Ready for checkin | |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
This is my first django ticket here. Please, forgive for possible mistakes.
Issue:
I want to be able to use a custom template engine (same DjangoTemplates, but with different settings). Multiple template engines seems to be a great feature, but it becomes not that usable with big projects that depend on third party packages (such as django-cms, wagtail, etc) - you have to tell each view/render to use the default engine, otherwise you get "Several DjangoTemplates backends are configured. You must select one explicitly." ImproperlyConfigured
exception.
Solution:
It would be really useful if it would be possible to mark one of the template engines as default and choose alternative engine where desired.
Changes to :meth:django.template.engine.get_default
and engine configuration (TEMPLATES
setting) would be really trivial. I could make a patch if approved.
Thank you (in any case)!
Change History (17)
comment:1 by , 8 years ago
comment:2 by , 8 years ago
@Aymeric Augustin:
Sure!
---
My settings:
TEMPLATES = [ # The default engine - a heavy one with a lot of context processors { 'NAME': 'default', 'BACKEND': 'django.template.backends.django.DjangoTemplates', 'DIRS': [], 'APP_DIRS': True, 'OPTIONS': { 'context_processors': [ 'django.contrib.auth.context_processors.auth', 'django.contrib.messages.context_processors.messages', 'django.template.context_processors.i18n', 'django.template.context_processors.request', 'django.template.context_processors.media', 'django.template.context_processors.static', 'sekizai.context_processors.sekizai', 'cms.context_processors.cms_settings', ], 'debug': True, } }, # Light engine - only very necessary things go here { 'NAME': 'light', 'BACKEND': 'django.template.backends.django.DjangoTemplates', 'DIRS': [], 'APP_DIRS': True, 'OPTIONS': { 'context_processors': [ 'django.contrib.auth.context_processors.auth', 'django.contrib.messages.context_processors.messages', 'django.template.context_processors.i18n', 'django.template.context_processors.request', 'django.template.context_processors.media', 'django.template.context_processors.static', ], 'debug': True, }, }, ]
---
Environment: Request Method: GET Request URL: http://localhost:8000/de-at/suchen/ Django Version: 1.8.7 Python Version: 2.7.6 Installed Applications: ('djangocms_admin_style', 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.redirects', 'django.contrib.staticfiles', 'django.contrib.sites', 'django.contrib.sitemaps', 'mptt', 'treebeard', 'menus', 'sekizai', 'easy_select2', 'easy_thumbnails', 'metatags', 'ckeditor', 'cmsplugin_filer_file', 'cmsplugin_filer_folder', 'cmsplugin_filer_link', 'cmsplugin_filer_image', 'cmsplugin_filer_teaser', 'cmsplugin_filer_video', 'cms', 'hvad', 'reversion', 'compressor', 'filer', 'rosetta', 'debug_toolbar') Installed Middleware: ('django.middleware.cache.UpdateCacheMiddleware', 'django.contrib.sessions.middleware.SessionMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', 'django.contrib.auth.middleware.AuthenticationMiddleware', 'django.contrib.messages.middleware.MessageMiddleware', 'django.contrib.redirects.middleware.RedirectFallbackMiddleware', 'django.middleware.locale.LocaleMiddleware', 'django.contrib.admindocs.middleware.XViewMiddleware', 'django.middleware.common.CommonMiddleware', 'cms.middleware.page.CurrentPageMiddleware', 'cms.middleware.user.CurrentUserMiddleware', 'cms.middleware.toolbar.ToolbarMiddleware', 'cms.middleware.language.LanguageCookieMiddleware', 'django.middleware.cache.FetchFromCacheMiddleware', 'debug_toolbar.middleware.DebugToolbarMiddleware') Traceback: File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response 164. response = response.render() File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/response.py" in render 158. self.content = self.rendered_content File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/response.py" in rendered_content 135. content = template.render(context, self._request) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/backends/django.py" in render 74. return self.template.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 210. return self._render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/test/utils.py" in instrumented_test_render 96. return self.nodelist.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 905. bit = self.render_node(node, context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render_node 919. return node.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render 135. return compiled_parent._render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/test/utils.py" in instrumented_test_render 96. return self.nodelist.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 905. bit = self.render_node(node, context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render_node 919. return node.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/classytags/core.py" in render 138. return self.render_tag(context, **kwargs) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/sekizai/templatetags/sekizai_tags.py" in render_tag 79. rendered_contents = nodelist.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 905. bit = self.render_node(node, context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render_node 919. return node.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/classytags/core.py" in render 138. return self.render_tag(context, **kwargs) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/sekizai/templatetags/sekizai_tags.py" in render_tag 79. rendered_contents = nodelist.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 905. bit = self.render_node(node, context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render_node 919. return node.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/classytags/core.py" in render 138. return self.render_tag(context, **kwargs) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/templatetags/cms_tags.py" in render_tag 681. rendered_contents = nodelist.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 905. bit = self.render_node(node, context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render_node 919. return node.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render 65. result = block.nodelist.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render 905. bit = self.render_node(node, context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in render_node 919. return node.render(context) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/classytags/core.py" in render 138. return self.render_tag(context, **kwargs) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/templatetags/cms_tags.py" in render_tag 308. content = get_placeholder_content(context, request, page, name, inherit, nodelist) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/templatetags/cms_tags.py" in get_placeholder_content 227. placeholder = _get_placeholder(current_page, page, context, name) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/templatetags/cms_tags.py" in _get_placeholder 191. placeholders = page.rescan_placeholders().values() File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/models/pagemodel.py" in rescan_placeholders 1378. placeholders = get_placeholders(self.get_template()) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/utils/placeholder.py" in get_placeholders 236. placeholders = _scan_placeholders(_get_nodelist(compiled_template)) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/utils/placeholder.py" in _scan_placeholders 203. placeholders += _extend_nodelist(node) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/utils/placeholder.py" in _extend_nodelist 260. _extend_blocks(extend_node, blocks) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/utils/placeholder.py" in _extend_blocks 288. parent = extend_node.get_parent(get_context()) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/cms/utils/placeholder.py" in get_context 40. context.template = Template('') File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/base.py" in __init__ 188. engine = Engine.get_default() File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/utils/lru_cache.py" in wrapper 125. result = user_function(*args, **kwds) File "/home/me/.virtualenvs/myenv/local/lib/python2.7/site-packages/django/template/engine.py" in get_default 83. "Several DjangoTemplates backends are configured. " Exception Type: ImproperlyConfigured at /de-at/suchen/ Exception Value: Several DjangoTemplates backends are configured. You must select one explicitly.
comment:3 by , 8 years ago
Version: | 1.10 → 1.8 |
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comment:4 by , 8 years ago
Right, this situation is described in this part of the documentation: https://docs.djangoproject.com/en/1.10/ref/templates/api/#loading-a-template (the first two paragraphs).
I suppose the transition could be smoothed by adopting a convention for determining the default Django templates engine, perhaps by deciding it the one called "django" (or similar) when there are multiple engines configured.
Can you start by reporting this issue to django-cms
? They're doing context.template = Template('')
which, per the current documentation, isn't supported.
comment:5 by , 8 years ago
@Aymeric Augustin:
Thanks! I have already tracked it down and reported an issue.
comment:6 by , 8 years ago
Resolution: | → needsinfo |
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Status: | new → closed |
Feel free to reopen if it turns out some change is needed in Djano after all.
comment:7 by , 8 years ago
Resolution: | needsinfo |
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Status: | closed → new |
django-crispy-forms seems to have the same problem when used in a Django project that has multiple template engines of the same backend configured. (I haven't yet tried with multiple engines of different backends.)
What are libraries supposed to use instead of Template('template content here')
? By definition they cannot know what template engines the projects that the library will be used in have configured.
comment:8 by , 8 years ago
Triage Stage: | Unreviewed → Accepted |
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Given the current API, we are effectively asking apps like django-cms or crispy-forms (any third-party app that wants to load and render a Django template using the project's settings) to require their users to specify some setting (like DJANGO_CMS_TEMPLATE_ENGINE
) if the project has more than one DjangoTemplate engine configured. This may be OK: it's explicit and gives the project fine-grained control per third-party app. On the downside, it's unlikely to be the obvious first-choice for the author of a third-party app; the obvious first choice is to just try instantiating Template
directly, and even worse, this will probably appear to work fine until they think to test (or more likely, one of their users reports a bug) with multiple configured DTL engines.
IMO currently engine-less instantiation of Template
is an attractive nuisance that appears easy and obvious and only breaks in edge cases, at which point the person who hits the problem (the project owner) has no reasonable way to fix it (without forking the third-party app).
I think we must do one of two things. We could a) deprecate and eventually remove engine-less instantiation of Template
altogether, removing the attractive nuisance and requiring everyone to always be explicit from the start. Or we could b) add a "default DTL engine" marker, as suggested in this ticket, so that when a third-party app does the easy and naive thing (directly instantiate Template
), a project owner with multiple DTL engines configured has some recourse to fix it without forking.
I think (b) may be the more practical solution, and kinder to our user base.
comment:9 by , 8 years ago
I also think (b) is the most practical solution.
This problem also manifested itself in other project such as django-filter.
comment:10 by , 8 years ago
As maintainer of both django-filter and crispy forms, I'd say I (too) am in favour of the b
solution, i.e. adopting the proposal.
If we were writing new code, requiring an explicit template engine would be fine, but we're seeing code that's been working fine — quite literally — for years that's leading to the error here.
What's more it's only (≈) 1 user in a 100 that configures multiple template engines so the point about it being an untested and surprising edge-case is exactly right.
comment:11 by , 8 years ago
Owner: | changed from | to
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Status: | new → assigned |
comment:13 by , 8 years ago
Has patch: | set |
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[PR
Adds a failing test case for the issue and a naive fix.
Here we just take the first DTL engine returned. Users should employ collections.OrderedDict if they need to control this prior to Python 3.6.
Need to add a note to the docs to that effect if the patch is acceptable.
Alternative proposals:
Have a naming convention. e.g. pick engine named 'default'
Add a specific OPTION to the config dict.
This is something of an edge case, and so, (IMO) 'pick the first' should be sufficient.
comment:14 by , 8 years ago
Patch needs improvement: | set |
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comment:16 by , 8 years ago
Triage Stage: | Accepted → Ready for checkin |
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You shouldn't hit this error unless the third party apps rely on deprecated or private APIs.
Can you provide the full stack trace for the exception you're getting?