Fixed #29188 -- Fixed ContentFile.size after a write().

django/core/files/base.py

@@ -149,6 +149,10 @@ class ContentFile(File):
     def close(self):
         pass
 
+    def write(self, data):
+        self.__dict__.pop('_size', None)  # Clear the computed size.
+        return self.file.write(data)
+
 
 def endswith_cr(line):
     """Return True if line (a text or byte string) ends with '\r'."""

tests/files/tests.py

@@ -206,6 +206,16 @@ class ContentFileTestCase(unittest.TestCase):
         with file.open() as f:
             self.assertEqual(f.read(), b'content')
 
+    def test_size_changing_after_writing(self):
+        """ContentFile.size changes after a write()."""
+        f = ContentFile('')
+        self.assertEqual(f.size, 0)
+        f.write('Test ')
+        f.write('string')
+        self.assertEqual(f.size, 11)
+        with f.open() as fh:
+            self.assertEqual(fh.read(), 'Test string')
+
 
 class InMemoryUploadedFileTests(unittest.TestCase):
     def test_open_resets_file_to_start_and_returns_context_manager(self):