Fixed #18166 -- Added form_kwargs support to formsets.

By specifying form_kwargs when instantiating the formset, or overriding
the `get_form_kwargs` method on a formset class, you can pass extra
keyword arguments to the underlying `Form` instances.

Includes tests and documentation update.

django/forms/formsets.py

@@ -54,13 +54,14 @@ class BaseFormSet(object):
     A collection of instances of the same Form class.
     """
     def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
-                 initial=None, error_class=ErrorList):
+                 initial=None, error_class=ErrorList, form_kwargs=None):
         self.is_bound = data is not None or files is not None
         self.prefix = prefix or self.get_default_prefix()
         self.auto_id = auto_id
         self.data = data or {}
         self.files = files or {}
         self.initial = initial
+        self.form_kwargs = form_kwargs or {}
         self.error_class = error_class
         self._errors = None
         self._non_form_errors = None
@@ -139,9 +140,16 @@ class BaseFormSet(object):
         Instantiate forms at first property access.
         """
         # DoS protection is included in total_form_count()
-        forms = [self._construct_form(i) for i in range(self.total_form_count())]
+        forms = [self._construct_form(i, **self.get_form_kwargs(i))
+                 for i in range(self.total_form_count())]
         return forms
 
+    def get_form_kwargs(self, index):
+        """
+        Return additional keyword arguments for each individual formset form.
+        """
+        return self.form_kwargs.copy()
+
     def _construct_form(self, i, **kwargs):
         """
         Instantiates and returns the i-th form instance in a formset.
@@ -184,6 +192,7 @@ class BaseFormSet(object):
             auto_id=self.auto_id,
             prefix=self.add_prefix('__prefix__'),
             empty_permitted=True,
+            **self.get_form_kwargs(None)
         )
         self.add_fields(form, None)
         return form

docs/topics/forms/formsets.txt

@@ -238,6 +238,8 @@ pre-filled, and is also used to determine how many forms are required. You
 will probably never need to override either of these methods, so please be
 sure you understand what they do before doing so.
 
+.. _empty_form:
+
 ``empty_form``
 ~~~~~~~~~~~~~~
 
@@ -533,6 +535,43 @@ default fields/attributes of the order and deletion fields::
     <tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" id="id_form-0-pub_date" /></td></tr>
     <tr><th><label for="id_form-0-my_field">My field:</label></th><td><input type="text" name="form-0-my_field" id="id_form-0-my_field" /></td></tr>
 
+Passing custom parameters to formset forms
+------------------------------------------
+
+Sometimes your form class takes custom parameters, like ``MyArticleForm``.
+You can pass this parameter when instantiating the formset::
+
+    >>> from django.forms.formsets import BaseFormSet
+    >>> from django.forms.formsets import formset_factory
+    >>> from myapp.forms import ArticleForm
+
+    >>> class MyArticleForm(ArticleForm):
+    ...     def __init__(self, *args, **kwargs):
+    ...         self.user = kwargs.pop('user')
+    ...         super(MyArticleForm, self).__init__(*args, **kwargs)
+
+    >>> ArticleFormSet = formset_factory(MyArticleForm)
+    >>> formset = ArticleFormSet(form_kwargs={'user': request.user})
+
+The ``form_kwargs`` may also depend on the specific form instance. The formset
+base class provides a ``get_form_kwargs`` method. The method takes a single
+argument - the index of the form in the formset. The index is ``None`` for the
+:ref:`empty_form`::
+
+    >>> from django.forms.formsets import BaseFormSet
+    >>> from django.forms.formsets import formset_factory
+
+    >>> class BaseArticleFormSet(BaseFormSet):
+    ...     def get_form_kwargs(self, index):
+    ...         kwargs = super(BaseArticleFormSet, self).get_form_kwargs(index)
+    ...         kwargs['custom_kwarg'] = index
+    ...         return kwargs
+
+
+.. versionadded:: 1.9
+
+    The ``form_kwargs`` argument was added.
+
 Using a formset in views and templates
 --------------------------------------
 

tests/forms_tests/tests/test_formsets.py

@@ -57,6 +57,12 @@ class SplitDateTimeForm(Form):
 SplitDateTimeFormSet = formset_factory(SplitDateTimeForm)
 
 
+class CustomKwargForm(Form):
+    def __init__(self, *args, **kwargs):
+        self.custom_kwarg = kwargs.pop('custom_kwarg')
+        super(CustomKwargForm, self).__init__(*args, **kwargs)
+
+
 class FormsFormsetTestCase(SimpleTestCase):
 
     def make_choiceformset(self, formset_data=None, formset_class=ChoiceFormSet,
@@ -114,6 +120,37 @@ class FormsFormsetTestCase(SimpleTestCase):
         self.assertFalse(formset.is_valid())
         self.assertFalse(formset.has_changed())
 
+    def test_form_kwargs_formset(self):
+        """
+        Test that custom kwargs set on the formset instance are passed to the
+        underlying forms.
+        """
+        FormSet = formset_factory(CustomKwargForm, extra=2)
+        formset = FormSet(form_kwargs={'custom_kwarg': 1})
+        for form in formset:
+            self.assertTrue(hasattr(form, 'custom_kwarg'))
+            self.assertEqual(form.custom_kwarg, 1)
+
+    def test_form_kwargs_formset_dynamic(self):
+        """
+        Test that form kwargs can be passed dynamically in a formset.
+        """
+        class DynamicBaseFormSet(BaseFormSet):
+            def get_form_kwargs(self, index):
+                return {'custom_kwarg': index}
+
+        DynamicFormSet = formset_factory(CustomKwargForm, formset=DynamicBaseFormSet, extra=2)
+        formset = DynamicFormSet(form_kwargs={'custom_kwarg': 'ignored'})
+        for i, form in enumerate(formset):
+            self.assertTrue(hasattr(form, 'custom_kwarg'))
+            self.assertEqual(form.custom_kwarg, i)
+
+    def test_form_kwargs_empty_form(self):
+        FormSet = formset_factory(CustomKwargForm)
+        formset = FormSet(form_kwargs={'custom_kwarg': 1})
+        self.assertTrue(hasattr(formset.empty_form, 'custom_kwarg'))
+        self.assertEqual(formset.empty_form.custom_kwarg, 1)
+
     def test_formset_validation(self):
         # FormSet instances can also have an error attribute if validation failed for
         # any of the forms.