Bug report

Bug description:

In 3.13 we changed ast.dump() to not show empty values (None or the empty list) by default. However, this is based purely on the value of individual attributes:

>>> ast.dump(ast.Name(id="x"))
"Name(id='x', ctx=Load())"
>>> ast.dump(ast.Name(id=None))
'Name(ctx=Load())'
>>> ast.dump(ast.Name(id=[]))
'Name(ctx=Load())'

Instead, this logic should look at the node's _field_types and use the same logic we use to determine whether to allow omitting the argument in calls to the constructor: elide None if the type is a union including None, elide [] if the type is a list, and elide Load() if the type is an expr_context.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-134718: Fix ast.dump() for empty non-default values #134926
• [3.14] gh-134718: Fix ast.dump() for empty non-default values (GH-134926) #134931
• gh-134718: Omit optional Load() values in ast.dump() #134934
• [3.13] gh-134718: Fix ast.dump() for empty non-default values (GH-134926) #134936