Add open method on S3Boto3StorageFile with test

storages/backends/s3boto3.py

@@ -105,8 +105,10 @@ class S3Boto3StorageFile(CompressedFileMixin, File):
     order to properly write the file to S3. Be sure to close the file
     in your application.
     """
-
     def __init__(self, name, mode, storage, buffer_size=None):
+        self._initialize(name, mode, storage, buffer_size)
+
+    def _initialize(self, name, mode, storage, buffer_size=None):
         if 'r' in mode and 'w' in mode:
             raise ValueError("Can't combine 'r' and 'w' in mode.")
         self._storage = storage
@@ -224,6 +226,16 @@ def _create_empty_on_close(self):
             else:
                 raise
 
+    def open(self, mode=None):
+        if not self.closed:
+            # keeping it consistent with django default file behaviour
+            self.seek(0)
+        elif mode != self._mode:
+            self._initialize(self.name, mode, self._storage, self.buffer_size)
+        else:
+            raise ValueError("The file cannot be reopened.")
+        return self
+
     def close(self):
         if self._is_dirty:
             self._flush_write_buffer()

tests/test_s3boto3.py

@@ -767,6 +767,25 @@ def test_override_init_argument(self):
         storage = s3boto3.S3Boto3Storage(location='foo2')
         self.assertEqual(storage.location, 'foo2')
 
+    def test_open_file(self):
+        filename = "file_to_open.txt"
+        file = self.storage.open(filename, "w")
+        file.write("foo")
+        file.close()
+        file.open()
+        self.assertEqual(file._mode, "w")
+        file.close()
+        file.open("r")
+        self.assertEqual(file._mode, "r")
+        assert(file.read(), "foo")
+        file.close()
+        file.open("a")
+        file.write("bar")
+        file.close()
+        file.open("r")
+        self.assertEqual(file.read(), "foobar")
+        file.close()
+
 
 class S3StaticStorageTests(TestCase):
     def setUp(self):