Fixes #24727 -- Prevented ClearableFileInput from masking exceptions on Python 2

django/forms/widgets.py

@@ -377,6 +377,14 @@ class ClearableFileInput(FileInput):
         """
         Return whether value is considered to be initial value.
         """
+        # hasattr() masks exceptions on Python 2.
+        if six.PY2:
+            try:
+                getattr(value, 'url')
+            except AttributeError:
+                return False
+            else:
+                return bool(value)
         return bool(value and hasattr(value, 'url'))
 
     def get_template_substitution_values(self, value):

tests/forms_tests/tests/test_widgets.py

@@ -1345,6 +1345,25 @@ class ClearableFileInputTests(TestCase):
         self.assertIn('my<div>file', output)
         self.assertNotIn('my<div>file', output)
 
+    def test_html_does_not_mask_exceptions(self):
+        """
+        A ClearableFileInput should not mask exceptions produced while
+        checking that it has a value.
+        """
+        @python_2_unicode_compatible
+        class FailingURLFieldFile(object):
+            @property
+            def url(self):
+                raise RuntimeError('Canary')
+
+            def __str__(self):
+                return 'value'
+
+        widget = ClearableFileInput()
+        field = FailingURLFieldFile()
+        with self.assertRaisesMessage(RuntimeError, 'Canary'):
+            widget.render('myfile', field)
+
     def test_clear_input_renders_only_if_not_required(self):
         """
         A ClearableFileInput with is_required=False does not render a clear