hdr: add _Header._header_part

Author: scanny

docx/parts/document.py

@@ -82,6 +82,10 @@ def get_style_id(self, style_or_name, style_type):
         """
         return self.styles.get_style_id(style_or_name, style_type)
 
+    def header_part(self, rId):
+        """Return |HeaderPart| related by *rId*."""
+        raise NotImplementedError
+
     @lazyproperty
     def inline_shapes(self):
         """

docx/section.py

@@ -295,7 +295,8 @@ def _has_header_part(self):
     @property
     def _header_part(self):
         """|HeaderPart| object containing content of this header."""
-        raise NotImplementedError
+        headerReference = self._sectPr.get_headerReference(WD_HEADER_FOOTER.PRIMARY)
+        return self._document_part.header_part(headerReference.rId)
 
     @property
     def _prior_header(self):

tests/test_section.py

@@ -471,6 +471,18 @@ def it_knows_when_it_has_a_header_part_to_help(self, has_header_part_fixture):
 
         assert has_header_part is expected_value
 
+    def it_provides_access_to_its_header_part_to_help(
+        self, document_part_, header_part_
+    ):
+        sectPr = element("w:sectPr/w:headerReference{w:type=default,r:id=rId8}")
+        document_part_.header_part.return_value = header_part_
+        header = _Header(sectPr, document_part_)
+
+        header_part = header._header_part
+
+        document_part_.header_part.assert_called_once_with("rId8")
+        assert header_part is header_part_
+
     def it_provides_access_to_the_prior_Header_to_help(
         self, request, document_part_, header_
     ):