Skip D401 for docstrings that start directly with a section.

docs/release_notes.rst

@@ -12,6 +12,7 @@ New Features
 
 * Add support for `property_decorators` config to ignore D401.
 * Add support for Python 3.10 (#554).
+* No longer emit D401 for sections at the start of docstrings (#556).
 
 6.1.1 - May 17th, 2021
 ---------------------------

src/pydocstyle/checker.py

@@ -504,6 +504,9 @@ def check_imperative_mood(self, function, docstring):  # def context
         "Returns the pathname ...".
 
         """
+        ctxs = list(self._get_section_contexts_autodetect(docstring))
+        if ctxs and ctxs[0].is_docstring_start:
+            return
         if (
             docstring
             and not function.is_test
@@ -587,6 +590,16 @@ def check_starts_with_this(self, function, docstring):
         if first_word.lower() == 'this':
             return violations.D404()
 
+    @staticmethod
+    def _is_at_docstring_start(context):
+        """Return whether a `SectionContext` occurs at the start of a docstring."""
+        return context.original_index == 1 and context.previous_line in [
+            '"',
+            "'",
+            '"""',
+            "'''",
+        ]
+
     @staticmethod
     def _is_docstring_section(context):
         """Check if the suspected context is really a section header.
@@ -639,7 +652,9 @@ def _is_docstring_section(context):
         )
 
         prev_line_looks_like_end_of_paragraph = (
-            prev_line_ends_with_punctuation or is_blank(context.previous_line)
+            prev_line_ends_with_punctuation
+            or is_blank(context.previous_line)
+            or context.is_docstring_start
         )
 
         return (
@@ -749,7 +764,10 @@ def _check_common_section(
             else:
                 yield violations.D410(capitalized_section)
 
-        if not is_blank(context.previous_line):
+        if (
+            not is_blank(context.previous_line)
+            and not context.is_docstring_start
+        ):
             yield violations.D411(capitalized_section)
 
         yield from cls._check_blanks_and_section_underline(
@@ -945,6 +963,7 @@ def _suspected_as_section(_line):
                 'line',
                 'following_lines',
                 'original_index',
+                'is_docstring_start',
                 'is_last_section',
             ),
         )
@@ -960,15 +979,18 @@ def _suspected_as_section(_line):
                 lines[i + 1 :],
                 i,
                 False,
+                False,
             )
             for i in suspected_section_indices
         )
-
-        # Now that we have manageable objects - rule out false positives.
         contexts = (
-            c for c in contexts if ConventionChecker._is_docstring_section(c)
+            c._replace(is_docstring_start=cls._is_at_docstring_start(c))
+            for c in contexts
         )
 
+        # Now that we have manageable objects - rule out false positives.
+        contexts = (c for c in contexts if cls._is_docstring_section(c))
+
         # Now we shall trim the `following lines` field to only reach the
         # next section name.
         for a, b in pairwise(contexts, None):
@@ -980,6 +1002,7 @@ def _suspected_as_section(_line):
                 a.line,
                 lines[a.original_index + 1 : end],
                 a.original_index,
+                a.is_docstring_start,
                 b is None,
             )
 

src/tests/test_cases/sections.py

@@ -6,6 +6,7 @@
 expect = expectation.expect
 
 
+_D212 = 'D212: Multi-line docstring summary should start at the first line'
 _D213 = 'D213: Multi-line docstring summary should start at the second line'
 _D400 = "D400: First line should end with a period (not '!')"
 
@@ -191,6 +192,21 @@ def section_name_in_first_line():  # noqa: D416
     """
 
 
+@expect(_D212)
+@expect("D400: First line should end with a period (not 's')")
+@expect("D415: First line should end with a period, question "
+        "mark, or exclamation point (not 's')")
+@expect("D205: 1 blank line required between summary line and description "
+        "(found 0)")
+def section_name_in_first_nonblank_line():  # noqa: D416
+    """
+    Returns
+    -------
+    A value of some sort.
+
+    """
+
+
 @expect(_D213)
 @expect("D405: Section name should be properly capitalized "
         "('Short Summary', not 'Short summary')")