bpo-36287: Make ast.dump() not output optional fields and attributes with default values. (GH-18843)

The default values for optional fields and attributes of AST nodes are now set
as class attributes (e.g. Constant.kind is set to None).

1 files changed, 26 insertions, 20 deletions

diff --git a/Lib/ast.py b/Lib/ast.py
index 9a3d380..0bce4a4 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -123,31 +123,36 @@ def dump(node, annotate_fields=True, include_attributes=False, *, indent=None):
             prefix = ''
             sep = ', '
         if isinstance(node, AST):
+            cls = type(node)
             args = []
             allsimple = True
             keywords = annotate_fields
-            for field in node._fields:
+            for name in node._fields:
                 try:
-                    value = getattr(node, field)
+                    value = getattr(node, name)
                 except AttributeError:
                     keywords = True
+                    continue
+                if value is None and getattr(cls, name, ...) is None:
+                    keywords = True
+                    continue
+                value, simple = _format(value, level)
+                allsimple = allsimple and simple
+                if keywords:
+                    args.append('%s=%s' % (name, value))
                 else:
-                    value, simple = _format(value, level)
-                    allsimple = allsimple and simple
-                    if keywords:
-                        args.append('%s=%s' % (field, value))
-                    else:
-                        args.append(value)
+                    args.append(value)
             if include_attributes and node._attributes:
-                for attr in node._attributes:
+                for name in node._attributes:
                     try:
-                        value = getattr(node, attr)
+                        value = getattr(node, name)
                     except AttributeError:
-                        pass
-                    else:
-                        value, simple = _format(value, level)
-                        allsimple = allsimple and simple
-                        args.append('%s=%s' % (attr, value))
+                        continue
+                    if value is None and getattr(cls, name, ...) is None:
+                        continue
+                    value, simple = _format(value, level)
+                    allsimple = allsimple and simple
+                    args.append('%s=%s' % (name, value))
             if allsimple and len(args) <= 3:
                 return '%s(%s)' % (node.__class__.__name__, ', '.join(args)), not args
             return '%s(%s%s)' % (node.__class__.__name__, prefix, sep.join(args)), False
@@ -170,9 +175,10 @@ def copy_location(new_node, old_node):
     attributes) from *old_node* to *new_node* if possible, and return *new_node*.
     """
     for attr in 'lineno', 'col_offset', 'end_lineno', 'end_col_offset':
-        if attr in old_node._attributes and attr in new_node._attributes \
-           and hasattr(old_node, attr):
-            setattr(new_node, attr, getattr(old_node, attr))
+        if attr in old_node._attributes and attr in new_node._attributes:
+            value = getattr(old_node, attr, None)
+            if value is not None:
+                setattr(new_node, attr, value)
     return new_node
 
 
@@ -191,7 +197,7 @@ def fix_missing_locations(node):
             else:
                 lineno = node.lineno
         if 'end_lineno' in node._attributes:
-            if not hasattr(node, 'end_lineno'):
+            if getattr(node, 'end_lineno', None) is None:
                 node.end_lineno = end_lineno
             else:
                 end_lineno = node.end_lineno
@@ -201,7 +207,7 @@ def fix_missing_locations(node):
             else:
                 col_offset = node.col_offset
         if 'end_col_offset' in node._attributes:
-            if not hasattr(node, 'end_col_offset'):
+            if getattr(node, 'end_col_offset', None) is None:
                 node.end_col_offset = end_col_offset
             else:
                 end_col_offset = node.end_col_offset