bpo-32911: Revert bpo-29463. (GH-7121) (GH-7197)

Remove the docstring attribute of AST types and restore docstring
expression as a first stmt in their body.

Co-authored-by: INADA Naoki <methane@users.noreply.github.com>

Author: serhiy-storchaka

Doc/library/ast.rst

@@ -151,10 +151,6 @@ and classes for traversing abstract syntax trees:
    .. versionchanged:: 3.5
       :class:`AsyncFunctionDef` is now supported.
 
-   .. versionchanged:: 3.7
-      The docstring is now exported from the node docstring field, instead of
-      the first body statement.
-
 
 .. function:: fix_missing_locations(node)
 

Doc/whatsnew/3.7.rst

@@ -2161,13 +2161,6 @@ Changes in Python Behavior
 Changes in the Python API
 -------------------------
 
-* ``Module``, ``FunctionDef``, ``AsyncFunctionDef``, and
-  ``ClassDef`` AST nodes now have the new ``docstring`` attribute.
-  The first statement in their body is not considered as a docstring
-  anymore.  ``co_firstlineno`` and ``co_lnotab`` of code object for class
-  and module are affected by this change. (Contributed by INADA Naoki and
-  Eugene Toder in :issue:`29463`.)
-
 * :meth:`socketserver.ThreadingMixIn.server_close` now waits until all
   non-daemon threads complete.  Set the new
   :attr:`socketserver.ThreadingMixIn.block_on_close` class attribute to

Include/Python-ast.h

@@ -46,7 +46,6 @@ struct _mod {
     union {
         struct {
             asdl_seq *body;
-            string docstring;
         } Module;
 
         struct {
@@ -81,7 +80,6 @@ struct _stmt {
             asdl_seq *body;
             asdl_seq *decorator_list;
             expr_ty returns;
-            string docstring;
         } FunctionDef;
 
         struct {
@@ -90,7 +88,6 @@ struct _stmt {
             asdl_seq *body;
             asdl_seq *decorator_list;
             expr_ty returns;
-            string docstring;
         } AsyncFunctionDef;
 
         struct {
@@ -99,7 +96,6 @@ struct _stmt {
             asdl_seq *keywords;
             asdl_seq *body;
             asdl_seq *decorator_list;
-            string docstring;
         } ClassDef;
 
         struct {
@@ -443,27 +439,26 @@ struct _withitem {
 };
 
 
-#define Module(a0, a1, a2) _Py_Module(a0, a1, a2)
-mod_ty _Py_Module(asdl_seq * body, string docstring, PyArena *arena);
+#define Module(a0, a1) _Py_Module(a0, a1)
+mod_ty _Py_Module(asdl_seq * body, PyArena *arena);
 #define Interactive(a0, a1) _Py_Interactive(a0, a1)
 mod_ty _Py_Interactive(asdl_seq * body, PyArena *arena);
 #define Expression(a0, a1) _Py_Expression(a0, a1)
 mod_ty _Py_Expression(expr_ty body, PyArena *arena);
 #define Suite(a0, a1) _Py_Suite(a0, a1)
 mod_ty _Py_Suite(asdl_seq * body, PyArena *arena);
-#define FunctionDef(a0, a1, a2, a3, a4, a5, a6, a7, a8) _Py_FunctionDef(a0, a1, a2, a3, a4, a5, a6, a7, a8)
+#define FunctionDef(a0, a1, a2, a3, a4, a5, a6, a7) _Py_FunctionDef(a0, a1, a2, a3, a4, a5, a6, a7)
 stmt_ty _Py_FunctionDef(identifier name, arguments_ty args, asdl_seq * body,
-                        asdl_seq * decorator_list, expr_ty returns, string
-                        docstring, int lineno, int col_offset, PyArena *arena);
-#define AsyncFunctionDef(a0, a1, a2, a3, a4, a5, a6, a7, a8) _Py_AsyncFunctionDef(a0, a1, a2, a3, a4, a5, a6, a7, a8)
+                        asdl_seq * decorator_list, expr_ty returns, int lineno,
+                        int col_offset, PyArena *arena);
+#define AsyncFunctionDef(a0, a1, a2, a3, a4, a5, a6, a7) _Py_AsyncFunctionDef(a0, a1, a2, a3, a4, a5, a6, a7)
 stmt_ty _Py_AsyncFunctionDef(identifier name, arguments_ty args, asdl_seq *
                              body, asdl_seq * decorator_list, expr_ty returns,
-                             string docstring, int lineno, int col_offset,
-                             PyArena *arena);
-#define ClassDef(a0, a1, a2, a3, a4, a5, a6, a7, a8) _Py_ClassDef(a0, a1, a2, a3, a4, a5, a6, a7, a8)
+                             int lineno, int col_offset, PyArena *arena);
+#define ClassDef(a0, a1, a2, a3, a4, a5, a6, a7) _Py_ClassDef(a0, a1, a2, a3, a4, a5, a6, a7)
 stmt_ty _Py_ClassDef(identifier name, asdl_seq * bases, asdl_seq * keywords,
-                     asdl_seq * body, asdl_seq * decorator_list, string
-                     docstring, int lineno, int col_offset, PyArena *arena);
+                     asdl_seq * body, asdl_seq * decorator_list, int lineno,
+                     int col_offset, PyArena *arena);
 #define Return(a0, a1, a2, a3) _Py_Return(a0, a1, a2, a3)
 stmt_ty _Py_Return(expr_ty value, int lineno, int col_offset, PyArena *arena);
 #define Delete(a0, a1, a2, a3) _Py_Delete(a0, a1, a2, a3)

Lib/ast.py

@@ -206,7 +206,15 @@ def get_docstring(node, clean=True):
     """
     if not isinstance(node, (AsyncFunctionDef, FunctionDef, ClassDef, Module)):
         raise TypeError("%r can't have docstrings" % node.__class__.__name__)
-    text = node.docstring
+    if not node.body:
+        return None
+    node = node.body[0].value
+    if isinstance(node, Str):
+        text = node.s
+    elif isinstance(node, Constant) and isinstance(node.value, str):
+        text = node.value
+    else:
+        return None
     if clean and text:
         import inspect
         text = inspect.cleandoc(text)