Django error: got multiple values for keyword argument

Question

I get the following error when instantiating a Django form with a the constructor overriden:

__init__() got multiple values for keyword argument 'collection_type' 

The __init__() function (shown below) is exactly as written this but with # code replaced with my logic. Asside from that I am essentially overriding the form's (which is a ModelForm) constructor.

def __init__(self, collection_type, user=None, parent=None, *args, **kwargs):     # code     super(self.__class__, self).__init__(*args, **kwargs) 

The call that creates the error is shown here:

form = CreateCollectionForm(     request.POST,      collection_type=collection_type,      parent=parent,      user=request.user ) 

I cannot see any reason why the error is popping up.

EDIT: Here is the full code for the constructor

def __init__(self, collection_type, user=None, parent=None, *args, **kwargs):     self.collection_type = collection_type     if self.collection_type == 'library':         self.user = user     elif self.collection_type == 'bookshelf' or self.collection_type == 'series':         self.parent = parent     else:         raise AssertionError, 'collection_type must be "library", "bookshelf" or "series"'     super(self.__class__, self).__init__(*args, **kwargs) 

EDIT: Stacktrace

Environment:  Request Method: POST Request URL: http://localhost:8000/forms/create_bookshelf/hello Django Version: 1.1.1 Python Version: 2.6.1 Installed Applications: ['django.contrib.auth',  'django.contrib.contenttypes',  'django.contrib.sessions',  'django.contrib.sites',  'libraries',  'users',  'books',  'django.contrib.admin',  'googlehooks',  'registration'] Installed Middleware: ('django.middleware.common.CommonMiddleware',  'django.contrib.sessions.middleware.SessionMiddleware',  'django.contrib.auth.middleware.AuthenticationMiddleware')   Traceback: File "/Library/Python/2.6/site-packages/django/core/handlers/base.py" in get_response   92.                 response = callback(request, *callback_args, **callback_kwargs) File "/Library/Python/2.6/site-packages/django/contrib/auth/decorators.py" in __call__   78.             return self.view_func(request, *args, **kwargs) File "/Users/marcus/Sites/marcuswhybrow.net/autolib/libraries/forms.py" in     create_collection   13.           form = CreateCollectionForm(request.POST,     collection_type=collection_type, user=request.user)  Exception Type: TypeError at /forms/create_bookshelf/hello Exception Value: __init__() got multiple values for keyword argument 'collection_type' 

Answer 1

You're passing the collection_type argument in as a keyword argument, because you specifically say collection_type=collection_type in your call to the form constructor. So Python includes it within the kwargs dictionary - but because you have also declared it as a positional argument in that function's definition, it attempts to pass it twice, hence the error.

However, what you're trying to do will never work. You can't have user=None, parent=None before the *args dictionary, as those are already kwargs, and args must always come before kwargs. The way to fix it is to drop the explicit definition of collection_type, user and parent, and extract them from kwargs within the function:

def __init__(self, *args, **kwargs):     collection_type = kwargs.pop('collection_type', None)     user = kwargs.pop('user', None)     parent = kwargs.pop('parent', None) 

Answer 2

It's pretty simple: you pass request.POST and only afterward you put argument for collection_type. Onto what request.POST will be put? There is not place for that. Watch this:

In [8]: class A:    ...:     def __init__(self, a, *args):    ...:         print a, args    ...:             ...:           In [9]: A(None, a=None) --------------------------------------------------------------------------- TypeError                                 Traceback (most recent call last)  /home/gruszczy/Programy/logbuilder/<ipython console> in <module>()  TypeError: __init__() got multiple values for keyword argument 'a' 

Move request.POST somewhere else in the call, but remember, that named arguments come after the ones, that aren't.