unknown encoding: cp0

If you receive this when deploying django on apache, it’s because you have something like:

print "Something %s" % value

The fix is to change it to:

print "Something %s" % str(value)

django create superuser automatically on syncdb

Found the following information here. Here’s how you can automatically create a superuser when syncing your db:

python manage.py dumpdata auth > initial_data.json 
python manage.py syncdb

Make sure to modify the initial.json file, if you want to change the name/mail of the superuser.

always specify fields for django’s ModelForm as a tuple

So, I had a model that had a FileField called path, for which I wanted a ModelForm. Do not do this:

class MyModelForm(ModelForm):
   class Meta:
      model = MyModel
      fields= ("path")

It led to a strange error, saying django.core.exceptions.FieldError: Unknown field(s) (a, p, t, h). Of course, the fix was to specify the fields like:

class MyModelForm(ModelForm):
   class Meta:
      model = MyModel
      fields= ("path",)

django FileField and random names

To ensure that an uploaded file will have a random name, use a custom storage object, like described here.

django override widget to be used by field

I wanted to override the widget used by one of my fields, in the admin. Here’s how I ended up doing:

class MyAdmin(admin.ModelAdmin):
  def formfield_for_dbfield(self,db_field,**kwargs):
     field = super(MyAdmin,self).formfield_for_dbfield(db_field,**kwargs)
     if db_field.name == "name_of_field_i_want_to_override":
        field.widget = MyCustomWidget
     return field

django modelformset disallow empty forms

In order to disallow empty forms from being submitted to a ModelFormSet, do this in your formset:

class MyModelFormSet(BaseModelFormSet):
  def __init__(self,*args,**kwargs):
    super(MyModelFormSet,self).__init__(*args,**kwargs)
    for form in self.forms:
      form.empty_permitted = False

django acces instance used by admin

If you find that you need to access the instance used by the admin, override get_form in your ModelAdmin subclass:

class MyAdmin(admin.ModelAdmin):
  def get_form(self, request, obj=None, **kwargs):
    self.object_instance = obj
    return super(MyAdmin,self).get_form(request,obj,**kwargs)

django generate json

An approach to generating custom JSON from your objects, mostly a repost of http://theoephraim.com/2011/04/json-encoding-custom-django-models/:

from django.utils.simplejson import JSONEncoder

class CustomObjectEncoder(JSONEncoder):
	def default(self, obj):
		if isinstance(obj,MyModel):
			return obj.to_dict()
		return JSONEncoder.default(self, obj)

class MyModel(models.Model):
  # how our custom json will look like
  def to_dict(self):
    return {"id":self.id,"label":self.name,"value":self.name}

# view that generates json
def autocomplete(request):
  mimetype = "application/javascript"
  # need to call list, because querysets are not serializable
  data = list(MyModel.objects.all())
  return HttpResponse(CustomObjectEncoder().encode(data),mimetype)