pythongh-103000: Optimise dataclasses asdict/astuple for common types (…

…python#103005)

Co-authored-by: Carl Meyer <carl@oddbird.net>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Lib/dataclasses.py

@@ -222,6 +222,29 @@ def __repr__(self):
 # https://bugs.python.org/issue33453 for details.
 _MODULE_IDENTIFIER_RE = re.compile(r'^(?:\s*(\w+)\s*\.)?\s*(\w+)')
 
+# Atomic immutable types which don't require any recursive handling and for which deepcopy
+# returns the same object. We can provide a fast-path for these types in asdict and astuple.
+_ATOMIC_TYPES = frozenset({
+ # Common JSON Serializable types
+ types.NoneType,
+ bool,
+ int,
+ float,
+ str,
+ # Other common types
+ complex,
+ bytes,
+ # Other types that are also unaffected by deepcopy
+ types.EllipsisType,
+ types.NotImplementedType,
+ types.CodeType,
+ types.BuiltinFunctionType,
+ types.FunctionType,
+ type,
+ range,
+ property,
+})
+
 # This function's logic is copied from "recursive_repr" function in
 # reprlib module to avoid dependency.
 def _recursive_repr(user_function):
@@ -1291,7 +1314,9 @@ class C:
 
 
 def _asdict_inner(obj, dict_factory):
- if _is_dataclass_instance(obj):
+ if type(obj) in _ATOMIC_TYPES:
+ return obj
+ elif _is_dataclass_instance(obj):
  result = []
  for f in fields(obj):
  value = _asdict_inner(getattr(obj, f.name), dict_factory)
@@ -1363,7 +1388,9 @@ class C:
 
 
 def _astuple_inner(obj, tuple_factory):
- if _is_dataclass_instance(obj):
+ if type(obj) in _ATOMIC_TYPES:
+ return obj
+ elif _is_dataclass_instance(obj):
  result = []
  for f in fields(obj):
  value = _astuple_inner(getattr(obj, f.name), tuple_factory)

Misc/NEWS.d/next/Library/2023-03-24-20-49-48.gh-issue-103000.6eVNZI.rst

@@ -0,0 +1,2 @@
+Improve performance of :func:`dataclasses.astuple` and
+:func:`dataclasses.asdict` in cases where the contents are common Python types.