Only use the alt text of image elements as a fallback

3 files changed, 30 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index a30c011..10d5334 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,9 @@
+# 1.5.0
+
+* Only use the alt text of image elements as a fallback. If an alt attribute is
+  returned from the function passed to mammoth.images.img_element, that value
+  will now be preferred to the alt text of the image element.
+
 # 1.4.19
 
 * Ignore w:u elements when w:val is missing.
diff --git a/mammoth/images.py b/mammoth/images.py
index 9dba353..21b9288 100644
--- a/mammoth/images.py
+++ b/mammoth/images.py
@@ -5,12 +5,13 @@ from . import html
 
 def img_element(func):
     def convert_image(image):
-        attributes = func(image).copy()
+        attributes = {}
         if image.alt_text:
             attributes["alt"] = image.alt_text
-            
+        attributes.update(func(image))
+
         return [html.element("img", attributes)]
-    
+
     return convert_image
 
 # Undocumented, but retained for backwards-compatibility with 0.3.x
@@ -21,7 +22,7 @@ inline = img_element
 def data_uri(image):
     with image.open() as image_bytes:
         encoded_src = base64.b64encode(image_bytes.read()).decode("ascii")
-    
+
     return {
         "src": "data:{0};base64,{1}".format(image.content_type, encoded_src)
     }
diff --git a/tests/images_tests.py b/tests/images_tests.py
index 49784d3..0ab29e1 100644
--- a/tests/images_tests.py
+++ b/tests/images_tests.py
@@ -66,3 +66,22 @@ class ImgElementTests:
         assert_that(result, is_sequence(
             has_attrs(attributes={"alt": "<alt>", "src": "<src>"}),
         ))
+
+    @istest
+    def test_image_alt_text_can_be_overridden_by_alt_attribute_returned_from_function(self):
+        image_bytes = b"abc"
+        image = mammoth.documents.Image(
+            alt_text="<alt>",
+            content_type="image/jpeg",
+            open=lambda: io.BytesIO(image_bytes),
+        )
+
+        @mammoth.images.img_element
+        def convert_image(image):
+            return {"alt": "<alt override>", "src": "<src>"}
+
+        result = convert_image(image)
+
+        assert_that(result, is_sequence(
+            has_attrs(attributes={"alt": "<alt override>", "src": "<src>"}),
+        ))