fix: default block width when document has no sections

src/docx/document.py

@@ -232,6 +232,9 @@ def tables(self) -> List[Table]:
     @property
     def _block_width(self) -> Length:
         """A |Length| object specifying the space between margins in last section."""
+        # No sectPr (some generators): same Letter defaults as None page/margin values.
+        if not self.sections:
+            return Emu(Inches(8.5) - Inches(1) - Inches(1))
         section = self.sections[-1]
         page_width = section.page_width or Inches(8.5)
         left_margin = section.left_margin or Inches(1)

tests/test_document.py

@@ -19,7 +19,7 @@
 from docx.section import Section, Sections
 from docx.settings import Settings
 from docx.shape import InlineShape, InlineShapes
-from docx.shared import Length
+from docx.shared import Inches, Length
 from docx.styles.styles import Styles
 from docx.table import Table
 from docx.text.paragraph import Paragraph
@@ -286,6 +286,17 @@ def it_determines_block_width_to_help(
         assert isinstance(width, Length)
         assert width == 3500
 
+    def it_uses_default_block_width_when_document_has_no_sections(
+        self, document: Document, sections_prop_: Mock
+    ):
+        # No sectPr: same Letter defaults as None page/margin (avoids sections[-1]).
+        sections_prop_.return_value = []
+
+        width = document._block_width
+
+        assert isinstance(width, Length)
+        assert width == Inches(8.5) - Inches(1) - Inches(1)
+
     # -- fixtures --------------------------------------------------------------------------------
 
     @pytest.fixture