From 48c394a6fc2594891f766293afec8f86d63e1015 Mon Sep 17 00:00:00 2001
From: Josh Schneier <josh.schneier@gmail.com>
Date: Tue, 5 Sep 2017 12:41:38 -0400
Subject: [PATCH] Fixed #28555 -- Made CharField convert whitespace-only values
 to the empty_value when strip is enabled.

---
 django/forms/fields.py                        |  7 +++---
 .../forms_tests/field_tests/test_charfield.py | 23 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/django/forms/fields.py b/django/forms/fields.py
index 40fdb24a10..805018786a 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -221,11 +221,12 @@ class CharField(Field):
 
     def to_python(self, value):
         """Return a string."""
+        if value not in self.empty_values:
+            value = str(value)
+            if self.strip:
+                value = value.strip()
         if value in self.empty_values:
             return self.empty_value
-        value = str(value)
-        if self.strip:
-            value = value.strip()
         return value
 
     def widget_attrs(self, widget):
diff --git a/tests/forms_tests/field_tests/test_charfield.py b/tests/forms_tests/field_tests/test_charfield.py
index 8f6a27f473..ad91070571 100644
--- a/tests/forms_tests/field_tests/test_charfield.py
+++ b/tests/forms_tests/field_tests/test_charfield.py
@@ -120,6 +120,29 @@ class CharFieldTest(FormFieldAssertionsMixin, SimpleTestCase):
         self.assertEqual(f.clean(' 1'), ' 1')
         self.assertEqual(f.clean('1 '), '1 ')
 
+    def test_strip_before_checking_empty(self):
+        """
+        A whitespace-only value, ' ', is stripped to an empty string and then
+        converted to the empty value, None.
+        """
+        f = CharField(required=False, empty_value=None)
+        self.assertIsNone(f.clean(' '))
+
+    def test_clean_non_string(self):
+        """CharField.clean() calls str(value) before stripping it."""
+        class StringWrapper:
+            def __init__(self, v):
+                self.v = v
+
+            def __str__(self):
+                return self.v
+
+        value = StringWrapper(' ')
+        f1 = CharField(required=False, empty_value=None)
+        self.assertIsNone(f1.clean(value))
+        f2 = CharField(strip=False)
+        self.assertEqual(f2.clean(value), ' ')
+
     def test_charfield_disabled(self):
         f = CharField(disabled=True)
         self.assertWidgetRendersTo(f, '<input type="text" name="f" id="id_f" disabled required />')