diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 9135b07c9f259a..f86111f330c844 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -6,6 +6,7 @@
import keyword
import builtins
import functools
+import collections
import _thread
@@ -1024,7 +1025,7 @@ def is_dataclass(obj):
return hasattr(cls, _FIELDS)
-def asdict(obj, *, dict_factory=dict):
+def asdict(obj, *, dict_factory=dict, transformers=None):
"""Return the fields of a dataclass instance as a new dictionary mapping
field names to field values.
@@ -1045,48 +1046,58 @@ class C:
"""
if not _is_dataclass_instance(obj):
raise TypeError("asdict() should be called on dataclass instances")
- return _asdict_inner(obj, dict_factory)
+ if transformers is None:
+ transformers = _DEFAULT_TRANFORMERS
+ else:
+ transformers = tuple(transformers) + _DEFAULT_TRANFORMERS
+
+ return _asdict_inner(obj, dict_factory, transformers)
+
+def _handle_dataclass(obj, asdict_inner):
+ result = []
+ for f in fields(obj):
+ value = asdict_inner(getattr(obj, f.name))
+ result.append((f.name, value))
+ return asdict_inner.dict_factory(result)
+
+def _handle_sequence(obj, asdict_inner):
+ return type(obj)(map(asdict_inner, obj))
+
+def _handle_dict(obj, asdict_inner):
+ return type(obj)(((asdict_inner(k), asdict_inner(v))
+ for k, v in obj.items()))
+
+def _handle_defaultdict(obj, asdict_inner):
+ return type(obj)(obj.default_factory,
+ ((asdict_inner(k), asdict_inner(v))
+ for k, v in obj.items()))
+
+def _handle_namedtuple(obj, asdict_inner):
+ return type(obj)(*map(asdict_inner, obj))
+
+_DEFAULT_TRANFORMERS = (
+ (_is_dataclass_instance, _handle_dataclass),
+ (lambda obj: isinstance(obj, tuple) and hasattr(obj, "_fields"),
+ _handle_namedtuple),
+ ((tuple, list), _handle_sequence),
+ (collections.defaultdict, _handle_defaultdict),
+ (dict, _handle_dict),
+)
+
+def _asdict_inner(obj, dict_factory, transformers):
+ def asdict_inner(obj):
+ for cond, transformer in transformers:
+ if isinstance(cond, (type, tuple)):
+ if isinstance(obj, cond):
+ return transformer(obj, asdict_inner)
+ elif cond(obj):
+ return transformer(obj, asdict_inner)
+ return copy.deepcopy(obj)
-def _asdict_inner(obj, dict_factory):
- if _is_dataclass_instance(obj):
- result = []
- for f in fields(obj):
- value = _asdict_inner(getattr(obj, f.name), dict_factory)
- result.append((f.name, value))
- return dict_factory(result)
- elif isinstance(obj, tuple) and hasattr(obj, '_fields'):
- # obj is a namedtuple. Recurse into it, but the returned
- # object is another namedtuple of the same type. This is
- # similar to how other list- or tuple-derived classes are
- # treated (see below), but we just need to create them
- # differently because a namedtuple's __init__ needs to be
- # called differently (see bpo-34363).
+ asdict_inner.dict_factory = dict_factory
- # I'm not using namedtuple's _asdict()
- # method, because:
- # - it does not recurse in to the namedtuple fields and
- # convert them to dicts (using dict_factory).
- # - I don't actually want to return a dict here. The the main
- # use case here is json.dumps, and it handles converting
- # namedtuples to lists. Admittedly we're losing some
- # information here when we produce a json list instead of a
- # dict. Note that if we returned dicts here instead of
- # namedtuples, we could no longer call asdict() on a data
- # structure where a namedtuple was used as a dict key.
-
- return type(obj)(*[_asdict_inner(v, dict_factory) for v in obj])
- elif isinstance(obj, (list, tuple)):
- # Assume we can create an object of this type by passing in a
- # generator (which is not true for namedtuples, handled
- # above).
- return type(obj)(_asdict_inner(v, dict_factory) for v in obj)
- elif isinstance(obj, dict):
- return type(obj)((_asdict_inner(k, dict_factory),
- _asdict_inner(v, dict_factory))
- for k, v in obj.items())
- else:
- return copy.deepcopy(obj)
+ return asdict_inner(obj)
def astuple(obj, *, tuple_factory=tuple):
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 037bf4c2214279..a59714ddf78c94 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -1652,6 +1652,18 @@ class C:
t = astuple(c, tuple_factory=list)
self.assertEqual(t, ['outer', T(1, ['inner', T(11, 12, 13)], 2)])
+ def test_helper_asdict_defaultdict(self):
+ @dataclass
+ class C:
+ d: dict
+
+ from collections import defaultdict
+ c = C(defaultdict(int))
+ self.assertEqual(asdict(c), {
+ 'd': defaultdict(int)
+ })
+
+
def test_dynamic_class_creation(self):
cls_dict = {'__annotations__': {'x': int, 'y': int},
}
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