Fixed #26905 -- Allowed using MultiValueDict-like objects as form data.

django/forms/widgets.py

@@ -13,7 +13,6 @@ from django.conf import settings
 from django.forms.utils import flatatt, to_current_timezone
 from django.templatetags.static import static
 from django.utils import datetime_safe, formats, six
-from django.utils.datastructures import MultiValueDict
 from django.utils.dates import MONTHS
 from django.utils.deprecation import (
     RemovedInDjango20Warning, RenameMethodsBase,
@@ -331,9 +330,11 @@ class MultipleHiddenInput(HiddenInput):
         return mark_safe('\n'.join(inputs))
 
     def value_from_datadict(self, data, files, name):
-        if isinstance(data, MultiValueDict):
-            return data.getlist(name)
-        return data.get(name)
+        try:
+            getter = data.getlist
+        except AttributeError:
+            getter = data.get
+        return getter(name)
 
 
 class FileInput(Input):
@@ -602,9 +603,11 @@ class SelectMultiple(Select):
         return mark_safe('\n'.join(output))
 
     def value_from_datadict(self, data, files, name):
-        if isinstance(data, MultiValueDict):
-            return data.getlist(name)
-        return data.get(name)
+        try:
+            getter = data.getlist
+        except AttributeError:
+            getter = data.get
+        return getter(name)
 
 
 @html_safe

tests/forms_tests/tests/test_forms.py

@@ -41,6 +41,11 @@ class PersonNew(Form):
     birthday = DateField()
 
 
+class MultiValueDictLike(dict):
+    def getlist(self, key):
+        return [self[key]]
+
+
 class FormsTestCase(SimpleTestCase):
     # A Form is a collection of Fields. It knows how to validate a set of data and it
     # knows how to render itself in a couple of default ways (e.g., an HTML table).
@@ -867,6 +872,12 @@ Java</label></li>
         f = SongForm(data)
         self.assertEqual(f.errors, {})
 
+        # SelectMultiple uses ducktyping so that MultiValueDictLike.getlist()
+        # is called.
+        f = SongForm(MultiValueDictLike({'name': 'Yesterday', 'composers': 'J'}))
+        self.assertEqual(f.errors, {})
+        self.assertEqual(f.cleaned_data['composers'], ['J'])
+
     def test_multiple_hidden(self):
         class SongForm(Form):
             name = CharField()
@@ -904,6 +915,12 @@ Java</label></li>
         self.assertEqual(f.cleaned_data['composers'], ['J', 'P'])
         self.assertEqual(f.cleaned_data['name'], 'Yesterday')
 
+        # MultipleHiddenInput uses ducktyping so that
+        # MultiValueDictLike.getlist() is called.
+        f = SongForm(MultiValueDictLike({'name': 'Yesterday', 'composers': 'J'}))
+        self.assertEqual(f.errors, {})
+        self.assertEqual(f.cleaned_data['composers'], ['J'])
+
     def test_escaping(self):
         # Validation errors are HTML-escaped when output as HTML.
         class EscapingForm(Form):