Documentation

In Python 3.13, AST node constructors now provide defaults for the omitted fields:

• Optional fields: default to None
• List fields: default to an empty list
• expr_context fields: default to Load()

Previously in Python 3.12 and earlier, these omitted fields would not exist as attributes, causing AttributeError when accessed.

These information can be found in What’s New In Python 3.13, but not in the ast documentation itself.

Since this is a significant behavioral change, it should be documented in the ast module documentation with a .. versionchanged:: 3.13 directive.

Linked PRs

• gh-140196: Added constructor behavior changes in ast.rst for python 3.13 #140243
• [3.14] gh-140196: Added constructor behavior changes in ast.rst for python 3.13 (GH-140243) #146351
• [3.13] gh-140196: Added constructor behavior changes in ast.rst for python 3.13 (GH-140243) #146354