ValueError with 1.6 on some pages only.

[mrmachine]

Here's the template code and traceback:

Template error:
In template /path/to/myproject/templates/myproject/base.html, error at line 84
   dictionary update sequence element #0 has length 22; 2 is required
   74 :     {% endif %}
   75 : 
   76 :     {% block icons %}
   77 :         <link rel="shortcut icon" href="{% static "myproject/images/icons/favicon.ico" %}">
   78 :         <link rel="apple-touch-icon" href="{% static "myproject/images/icons/apple-touch-icon.png" %}">
   79 :         <link rel="apple-touch-icon-precomposed" href="{% static "myproject/images/icons/apple-touch-icon-precomposed.png" %}">
   80 :     {% endblock icons %}
   81 : {% endblock %}
   82 : 
   83 : {% block base_css %}
   84 :      {% compress css file %} 
   85 :         <link rel="stylesheet" href="{% static "bootstrap/dist/css/bootstrap.css" %}">
   86 :         <link rel="stylesheet" href="{% static "font-awesome/css/font-awesome.css" %}">
   87 :         <link rel="stylesheet" href="{% static "slick-carousel/slick/slick.css" %}">
   88 :         <link type="text/less" rel="stylesheet" href="{% static "myproject/less/main.less" %}">
   89 :     {% endcompress %}
   90 : {% endblock %}
   91 : 
   92 : {% block head_js %}
   93 :     {% compress js file %}
   94 :         <script src="{% static "modernizr/modernizr.js" %}"></script>

Traceback:
File "/path/to/venv/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  111.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/path/to/venv/lib/python2.7/site-packages/django/db/transaction.py" in inner
  394.                 return func(*args, **kwargs)
File "/path/to/venv/src/django-multiurl/multiurl.py" in multiview
  72.                     response = match.func(request, *match.args, **match.kwargs)
File "/path/to/venv/src/django-multiurl/multiurl.py" in multiview
  72.                     response = match.func(request, *match.args, **match.kwargs)
File "/path/to/venv/lib/python2.7/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  21.                 return view_func(request, *args, **kwargs)
File "/path/to/myproject/research_projects/views.py" in document
  38.         return render_to_response(material.layout.template_name, c)
File "/path/to/venv/lib/python2.7/site-packages/django/shortcuts.py" in render_to_response
  25.     return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader.py" in render_to_string
  172.         return t.render(Context(dictionary))
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  148.             return self._render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  65.                 result = block.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  65.                 result = block.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/compressor/templatetags/compress.py" in render
  127.         return self.render_compressed(context, self.kind, self.mode, forced=forced)
File "/path/to/venv/lib/python2.7/site-packages/compressor/templatetags/compress.py" in render_compressed
  94.         compressor = self.get_compressor(context, kind)
File "/path/to/venv/lib/python2.7/site-packages/compressor/templatetags/compress.py" in get_compressor
  39.             content=self.get_original_content(context), context=context)
File "/path/to/venv/lib/python2.7/site-packages/compressor/templatetags/compress.py" in get_original_content
  119.         return self.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  65.                 result = block.nodelist.render(context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/path/to/venv/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/path/to/venv/lib/python2.7/site-packages/compressor/templatetags/compress.py" in render
  127.         return self.render_compressed(context, self.kind, self.mode, forced=forced)
File "/path/to/venv/lib/python2.7/site-packages/compressor/templatetags/compress.py" in render_compressed
  103.         rendered_output = compressor.output(mode, forced=forced)
File "/path/to/venv/lib/python2.7/site-packages/compressor/css.py" in output
  49.                     ret.append(subnode.output(*args, **kwargs))
File "/path/to/venv/lib/python2.7/site-packages/compressor/css.py" in output
  51.         return super(CssCompressor, self).output(*args, **kwargs)
File "/path/to/venv/lib/python2.7/site-packages/compressor/base.py" in output
  318.             return self.handle_output(mode, filtered_output, forced)
File "/path/to/venv/lib/python2.7/site-packages/compressor/base.py" in handle_output
  326.             return output_func(mode, content, forced, basename)
File "/path/to/venv/lib/python2.7/site-packages/compressor/base.py" in output_file
  340.         return self.render_output(mode, {"url": url})
File "/path/to/venv/lib/python2.7/site-packages/compressor/base.py" in render_output
  364.             final_context = self.context.flatten()
File "/path/to/venv/lib/python2.7/site-packages/django/template/context.py" in flatten
  106.             flat.update(d)

Exception Type: ValueError at /foo/
Exception Value: dictionary update sequence element #0 has length 22; 2 is required

The following code appears to be trying to target Django 1.8 by checking for Context.flatten(), even though that method was introduced in Django 1.7, which is what I am using.

django-compressor/compressor/base.py

Lines 342 to 347 in 7043dc9

	if hasattr(self.context, 'flatten'):
	# Django 1.8 complains about Context being passed to its
	# Template.render function.
	final_context = self.context.flatten()
	else:
	final_context = self.context

Changing it from:

        if hasattr(self.context, 'flatten'):
            # Django 1.8 complains about Context being passed to its
            # Template.render function.
            final_context = self.context.flatten()
        else:
            final_context = self.context

to:

        if django.VERSION < (1, 8):
            final_context = self.context
        else:
            # Django 1.8 complains about Context being passed to its
            # Template.render function.
            final_context = self.context.flatten()

seems to fix it for me.

[diox]

Hi,

Thanks for the bug report. Weird that it fails, I suppose our tests don't cover a specific context use case.

I'll try to look into that if I have the time, but since support for Django 1.7 or below has been removed in the develop version (as Django dropped 1.7 support recently), it's unlikely we'll fix it.

[cyberstar]

Hi @mrmachine , @diox! I've met the same issue. The bug is in Django itself. It is fixed for Django >=1.9, here is the pr and a discussion in django-cms/django-classy-tags#33 PR.

Related Django issue #26041 (https://code.djangoproject.com/ticket/26041) (the latest, but it has links to previous (original) issue.

I hope this will help.

[AaronGhent]

im getting a very similar error with django 1.8.10 exact same problem

ValueError at /
dictionary update sequence element #1 has length 1; 2 is required

just using

final_context = self.context

seems to fix it

[dmarcelino]

I'm using django 1.10 with django-categories and after replacing css for sass I also hit the issue described here, namely:

Exception Type: ValueError
Exception Value: dictionary update sequence element #0 has length 1; 2 is required
Exception Location: /Users/dario/development/python/ptexport/.venv/lib/python3.5/site-packages/django/template/context.py in flatten, line 122

Expanding on @mrmachine's proposal, the following fix works for me (though I'm not sure if it's the most appropriate):

from django import VERSION
...
        if VERSION < (1, 8) or VERSION > (1, 9):
            final_context = self.context
        else:
            # Django 1.8 complains about Context being passed to its
            # Template.render function.
            final_context = self.context.flatten()

[dmarcelino]

BTW, in my case, the view code that causes the issue is in categories/views.py#L20-L44:

def category_detail(request, path, template_name='categories/category_detail.html', extra_context={}):
    path_items = path.strip('/').split('/')
    if len(path_items) >= 2:
        category = get_object_or_404(
            Category,
            slug__iexact=path_items[-1],
            level=len(path_items) - 1,
            parent__slug__iexact=path_items[-2])
    else:
        category = get_object_or_404(
            Category,
            slug__iexact=path_items[-1],
            level=len(path_items) - 1)

    templates = []
    while path_items:
        templates.append('categories/%s.html' % '_'.join(path_items))
        path_items.pop()
    templates.append(template_name)

    context = RequestContext(request)
    context.update({'category': category})
    if extra_context:
        context.update(extra_context)
    return HttpResponse(select_template(templates).render(context))

[dmarcelino]

In my project I ended up modifying the above view code due to another issue. Afterwards I tried re-installing django-compressor without any patch and this time it worked fine. The main changes were:

context = RequestContext(request)
...
return HttpResponse(select_template(templates).render(context))

was changed to:

context = {}
...
return HttpResponse(select_template(templates).render(context, request))

Not sure what are the ramifications of this but it inadvertently fixed my issue.

[trawick]

Django 1.8.17, django-compressor-2.1 rcssmin-1.0.6 rjsmin-1.0.12

For one response I found, I'm getting ValueError: dictionary update sequence element #0 has length 8; 2 is required; just using final_context = self.context seems to fix it.

I also had the issue with django-compressor 1.6.

[cisarpavel]

Got same error with django 1.10.5. Fix using

    def render_output(self, mode, context=None):
        """
        Renders the compressor output with the appropriate template for
        the given mode and template context.
        """
        # Just in case someone renders the compressor outside
        # the usual template rendering cycle
        if 'compressed' not in self.context:
            self.context['compressed'] = {}
    
        self.context['compressed'].update(context or {})
        self.context['compressed'].update(self.extra_context)
        if VERSION < (1, 8) or VERSION > (1, 9):
            # Django 1.8 complains about Context being passed to its
            # Template.render function.
            final_context = self.context
        else:
            final_context = self.context.flatten()
    
        post_compress.send(sender=self.__class__, type=self.type,
                           mode=mode, context=final_context)
        template_name = self.get_template_name(mode)
        return render_to_string(template_name, context=final_context)

works for me.

[karyon]

hi, can you open a pull request?

[cisarpavel]

Unfortunatelly this solution seems to have problem with django 1.8. #836
Probably not totaly correct way.

[karyon]

I investigated this, here are my findings:

• There is a bug in django 1.8 in the flatten method (see https://code.djangoproject.com/ticket/24765). It has been fixed in django 1.9. The solution is simply to not use the flatten method (Do not use flatten on django 1.8 #850) in django 1.8, since passing Contexts to the render method still works there.
• For django 1.10, i don't know what the problem is that's observed by @dmarcelino and @cisarpavel and likely in https://code.djangoproject.com/ticket/26041. I haven't been able to reproduce it. Simply not calling flatten is likely not the correct solution since we would then pass a context into the render function, a feature that has been explicitly removed in django 1.10. i suspect that works by pure chance for very simple contexts.

so yeah, if anyone could help me reproducing this in django 1.10, that would help.

[nmashton]

Following up on @trawick's earlier comment, in my Django 1.11 project using django-compressor 2.2, I am still having this problem.

Whereas he found that just using final_context = self.context seemed to fix it, I'm finding that I need to do more work, specifically, flattening the inner contents of self.context.dicts before flattening self.context:

dicts = self.context.dicts
self.context.dicts = [
    d.flatten() for d in dicts
    if hasattr(d, 'flatten')
]
final_context = self.context.flatten()

[karyon]

if you could tell me how to reproduce this or even better, give me a repro case, that would be grand. or, actually, even better, create a failing test for this :)