Add support for passing extra parameters to the form constructor (FormPreview)

docs/preview.rst

@@ -139,3 +139,5 @@ Optional methods
 .. automethod:: FormPreview.security_hash
 
 .. automethod:: FormPreview.failed_hash
+
+.. automethod:: FormPreview.form_extra_params

formtools/preview.py

@@ -51,7 +51,8 @@ def unused_name(self, name):
     def preview_get(self, request):
         "Displays the form"
         f = self.form(auto_id=self.get_auto_id(),
-                      initial=self.get_initial(request))
+                      initial=self.get_initial(request),
+                      **self.form_extra_params(request))
         return render(request, self.form_template, self.get_context(request, f))
 
     def preview_post(self, request):
@@ -61,7 +62,10 @@ def preview_post(self, request):
         """
         # Even if files are not supported in preview, we still initialize files
         # to give a chance to process_preview to access files content.
-        f = self.form(data=request.POST, files=request.FILES, auto_id=self.get_auto_id())
+        f = self.form(data=request.POST,
+                      files=request.FILES,
+                      auto_id=self.get_auto_id(),
+                      **self.form_extra_params(request))
         context = self.get_context(request, f)
         if f.is_valid():
             self.process_preview(request, f, context)
@@ -79,7 +83,7 @@ def post_post(self, request):
         """
         Validates the POST data. If valid, calls done(). Else, redisplays form.
         """
-        form = self.form(request.POST, auto_id=self.get_auto_id())
+        form = self.form(request.POST, auto_id=self.get_auto_id(), **self.form_extra_params(request))
         if form.is_valid():
             if not self._check_security_hash(
                     request.POST.get(self.unused_name('hash'), ''),
@@ -158,6 +162,14 @@ def failed_hash(self, request):
         """
         return self.preview_post(request)
 
+    def form_extra_params(self, request):
+        """
+        Extra parameters to pass to the form constructor.
+        Returns a dictionary.
+        By default, returns an empty dictionary.
+        """
+        return {}
+
     # METHODS SUBCLASSES MUST OVERRIDE ########################################
 
     def done(self, request, cleaned_data):

tests/forms.py

@@ -7,6 +7,10 @@ class TestForm(forms.Form):
     bool1 = forms.BooleanField(required=False)
     date1 = forms.DateField(required=False)
 
+    def __init__(self, *args, **kwargs):
+        self.request = kwargs.pop('request', None)
+        super(TestForm, self).__init__(*args, **kwargs)
+
 
 class HashTestForm(forms.Form):
     name = forms.CharField()

tests/tests.py

@@ -32,6 +32,9 @@ def get_context(self, request, form):
     def get_initial(self, request):
         return {'field1': 'Works!'}
 
+    def form_extra_params(self, request):
+        return {'request': request}
+
     def done(self, request, cleaned_data):
         return http.HttpResponse(success_string)
 
@@ -64,7 +67,7 @@ def test_parse_params_takes_request_object(self):
 
     def test_unused_name(self):
         """
-        Verifies name mangling to get uniue field name.
+        Verifies name mangling to get unique field name.
         """
         self.assertEqual(self.preview.unused_name('field1'), 'field1__')