bpo-37950: Fix ast.dump() when call with incompletely initialized node. (GH-15510)

1 files changed, 24 insertions, 15 deletions

diff --git a/Lib/ast.py b/Lib/ast.py
index 1e639d1..5ab023f 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -98,26 +98,35 @@ def literal_eval(node_or_string):
 
 def dump(node, annotate_fields=True, include_attributes=False):
     """
-    Return a formatted dump of the tree in *node*.  This is mainly useful for
-    debugging purposes.  The returned string will show the names and the values
-    for fields.  This makes the code impossible to evaluate, so if evaluation is
-    wanted *annotate_fields* must be set to False.  Attributes such as line
+    Return a formatted dump of the tree in node.  This is mainly useful for
+    debugging purposes.  If annotate_fields is true (by default),
+    the returned string will show the names and the values for fields.
+    If annotate_fields is false, the result string will be more compact by
+    omitting unambiguous field names.  Attributes such as line
     numbers and column offsets are not dumped by default.  If this is wanted,
-    *include_attributes* can be set to True.
+    include_attributes can be set to true.
     """
     def _format(node):
         if isinstance(node, AST):
-            fields = [(a, _format(b)) for a, b in iter_fields(node)]
-            rv = '%s(%s' % (node.__class__.__name__, ', '.join(
-                ('%s=%s' % field for field in fields)
-                if annotate_fields else
-                (b for a, b in fields)
-            ))
+            args = []
+            keywords = annotate_fields
+            for field in node._fields:
+                try:
+                    value = getattr(node, field)
+                except AttributeError:
+                    keywords = True
+                else:
+                    if keywords:
+                        args.append('%s=%s' % (field, _format(value)))
+                    else:
+                        args.append(_format(value))
             if include_attributes and node._attributes:
-                rv += fields and ', ' or ' '
-                rv += ', '.join('%s=%s' % (a, _format(getattr(node, a)))
-                                for a in node._attributes)
-            return rv + ')'
+                for a in node._attributes:
+                    try:
+                        args.append('%s=%s' % (a, _format(getattr(node, a))))
+                    except AttributeError:
+                        pass
+            return '%s(%s)' % (node.__class__.__name__, ', '.join(args))
         elif isinstance(node, list):
             return '[%s]' % ', '.join(_format(x) for x in node)
         return repr(node)