[Django]-PlaceholderAdmin throws <lambda>() takes exactly 1 argument (2 given)

This issue is caused when you are not subclassing the PlaceholderAdminField in your admin class.

For example:

from cms.admin.placeholderadmin import PlaceholderAdmin
from cms.models.fields import PlaceholderField

class MyModel(models.Model):
    name = models.CharField(max_length=100)
    sidebar = PlaceholderField('sidebar')

class MyAdmin(PlaceholderAdmin):
    """ Put your usual admin stuff here. If you use fieldset,
    include the sidebar as its own tuple """
    fieldsets = (
        (None, {
            'fields': ('name',),
        }),

        ('Sidebar', {
            'classes': ('plugin-holder', 'plugin-holder-nopage'),
            'fields': ('sidebar',)
        }),
    )
admin.site.register(MyModel, MyAdmin)

Well, this appears to be a bug in Django-CMS. I’ve never used it, but looking at the code, it’s clear that the default formfield for PlaceholderField creates a lambda which takes a single argument – a queryset, but the render function for that formfield calls the lambda with two arguments – the request, and the queryset.

Probably the best way to fix this is to define your own subclass of PlaceholderField which redefines the formfield method so it returns a correct lambda:

class FixedPlaceholderField(PlaceholderField):
    def formfield(self, **kwargs):
        return self.formfield_for_admin(None, lambda request, qs: qs, **kwargs)

and use this field in your model instead.

If this fixes it, it’s probably worth raising a bug in Django-CMS.

Ok. I’ve solved the problem for me. I still don’t know what was happening but maybe my answer will help you figure it out ;).
I’ve used a method:

def formfield_for_dbfield(self, db_field, **kwargs):
    ...

which substituted one text field into TinyMCE editor. When I removed the whole method the problem vanished. If I have time later on maybe I’ll try to dig into it a little bit deeper.
I’m still not convinced that that was the only problem. I have a hunch that it also might be something with data because I’ve filled placeholder with text plugin from code.

Hope it helps somehow.