fix: python-openxml#455 Increment max-id, don't fill gaps

scanny · scanny · commit bdf4c369cb5e · 2018-08-18T13:50:31.000-07:00
While this may not work in all cases, it is less ugly than arbitrarily
boosting the id value as suggested. A general-case fix will have to wait
for access to headers and footers. It definitely reduces the likelihood
of a collision.
diff --git a/docx/parts/document.py b/docx/parts/document.py
@@ -96,16 +96,17 @@ def new_pic_inline(self, image_descriptor, width, height):
 
     @property
     def next_id(self):
-        """
-        The next available positive integer id value in this document. Gaps
-        in id sequence are filled. The id attribute value is unique in the
-        document, without regard to the element type it appears on.
+        """Next available positive integer id value in this document.
+
+        Calculated by incrementing maximum existing id value. Gaps in the
+        existing id sequence are not filled. The id attribute value is unique
+        in the document, without regard to the element type it appears on.
         """
         id_str_lst = self._element.xpath('//@id')
         used_ids = [int(id_str) for id_str in id_str_lst if id_str.isdigit()]
-        for n in range(1, len(used_ids)+2):
-            if n not in used_ids:
-                return n
+        if not used_ids:
+            return 1
+        return max(used_ids) + 1
 
     @lazyproperty
     def numbering_part(self):
diff --git a/tests/parts/test_document.py b/tests/parts/test_document.py
@@ -1,8 +1,6 @@
 # encoding: utf-8
 
-"""
-Test suite for the docx.parts.document module
-"""
+"""Test suite for the docx.parts.document module"""
 
 from __future__ import absolute_import, print_function, unicode_literals
 
@@ -198,8 +196,15 @@ def inline_shapes_fixture(self, request, InlineShapes_):
         return document, InlineShapes_, body_elm
 
     @pytest.fixture(params=[
-        ((), 1), ((1,), 2), ((2,), 1), ((1, 2, 3), 4), ((1, 2, 4), 3),
-        ((0, 0), 1), ((0, 0, 1, 3), 2), (('foo', 1, 2), 3), ((1, 'bar'), 2)
+        ((), 1),
+        ((1,), 2),
+        ((2,), 3),
+        ((1, 2, 3), 4),
+        ((1, 2, 4), 5),
+        ((0, 0), 1),
+        ((0, 0, 1, 3), 4),
+        (('foo', 1, 2), 3),
+        ((1, 'bar'), 2)
     ])
     def next_id_fixture(self, request):
         existing_ids, expected_id = request.param
