hdr: add _BaseHeaderFooter.is_linked_to_p.. getter

Author: scanny

docx/section.py

@@ -218,6 +218,25 @@ def __init__(self, sectPr, document_part):
         self._sectPr = sectPr
         self._document_part = document_part
 
+    @property
+    def is_linked_to_previous(self):
+        """True if this header/footer uses the definition from the preceding section.
+
+        False if this header/footer has an explicit definition.
+
+        Assigning ``True`` to this property removes the header/footer definition for
+        this section, causing it to "inherit" the corresponding definition of the prior
+        section. Assigning ``False`` causes a new, empty definition to be added for this
+        section, but only if no definition is already present.
+        """
+        # ---absence of a header/footer part indicates "linked" behavior---
+        return not self._has_definition
+
+    @property
+    def _has_definition(self):
+        """True if this header/footer has a related part containing its definition."""
+        raise NotImplementedError("must be implemented by each subclass")
+
 
 class _Footer(_BaseHeaderFooter):
     """Page footer."""

tests/test_section.py

@@ -9,7 +9,7 @@
 from docx.enum.section import WD_ORIENT, WD_SECTION
 from docx.parts.document import DocumentPart
 from docx.parts.hdrftr import HeaderPart
-from docx.section import _Footer, _Header, Section, Sections
+from docx.section import _BaseHeaderFooter, _Footer, _Header, Section, Sections
 from docx.shared import Inches
 
 from .unitutil.cxml import element, xml
@@ -358,6 +358,33 @@ def header_(self, request):
         return instance_mock(request, _Header)
 
 
+class Describe_BaseHeaderFooter(object):
+
+    def it_knows_when_its_linked_to_the_previous_header(
+        self, is_linked_get_fixture, _has_definition_prop_
+    ):
+        has_definition, expected_value = is_linked_get_fixture
+        _has_definition_prop_.return_value = has_definition
+        header = _BaseHeaderFooter(None, None)
+
+        is_linked = header.is_linked_to_previous
+
+        assert is_linked is expected_value
+
+    # fixtures -------------------------------------------------------
+
+    @pytest.fixture(params=[(False, True), (True, False)])
+    def is_linked_get_fixture(self, request):
+        has_definition, expected_value = request.param
+        return has_definition, expected_value
+
+    # fixture components ---------------------------------------------
+
+    @pytest.fixture
+    def _has_definition_prop_(self, request):
+        return property_mock(request, _BaseHeaderFooter, "_has_definition")
+
+
 class Describe_Header(object):
 
     def it_knows_when_its_linked_to_the_previous_header(