Support dataclass in MSONable protocol.

.pre-commit-config.yaml

@@ -1,7 +1,7 @@
 exclude: ^(docs|.*test_files|cmd_line|dev_scripts)
 
 default_language_version:
-  python: python3.8
+  python: python3.9
 
 ci:
   autoupdate_schedule: monthly

monty/json.py

@@ -44,6 +44,12 @@
 except ImportError:
     orjson = None  # type: ignore
 
+try:
+    import dataclasses
+except ImportError:
+    dataclasses = None  # type: ignore
+
+
 __version__ = "3.0.0"
 
 
@@ -140,6 +146,10 @@ def recursive_as_dict(obj):
                 return {kk: recursive_as_dict(vv) for kk, vv in obj.items()}
             if hasattr(obj, "as_dict"):
                 return obj.as_dict()
+            if dataclasses is not None and dataclasses.is_dataclass(obj):
+                d = dataclasses.asdict(obj)
+                d.update({"@module": obj.__class__.__module__, "@class": obj.__class__.__name__})
+                return d
             return obj
 
         for c in args:
@@ -407,13 +417,16 @@ def process_decoded(self, d):
                         return UUID(d["string"])
 
                     mod = __import__(modname, globals(), locals(), [classname], 0)
+
                     if hasattr(mod, classname):
                         cls_ = getattr(mod, classname)
                         data = {k: v for k, v in d.items() if not k.startswith("@")}
                         if hasattr(cls_, "from_dict"):
                             return cls_.from_dict(data)
                         if pydantic is not None and issubclass(cls_, pydantic.BaseModel):  # pylint: disable=E1101
                             return cls_(**data)
+                        if dataclasses is not None and dataclasses.is_dataclass(cls_):
+                            return cls_(**data)
                 elif np is not None and modname == "numpy" and classname == "array":
                     if d["dtype"].startswith("complex"):
                         return np.array(

tests/test_json.py

@@ -5,6 +5,7 @@
 import os
 import pathlib
 import unittest
+import dataclasses
 from enum import Enum
 
 import numpy as np
@@ -107,6 +108,18 @@ class ClassContainingNumpyArray(MSONable):
     def __init__(self, np_a):
         self.np_a = np_a
 
+@dataclasses.dataclass
+class Point:
+    x: float = 1
+    y: float = 2
+
+class Coordinates(MSONable):
+
+    def __init__(self, points):
+        self.points = points
+
+    def __str__(self):
+        return str(self.points)
 
 class MSONableTest(unittest.TestCase):
     def setUp(self):
@@ -652,6 +665,15 @@ class ModelWithMSONable(BaseModel):
         assert isinstance(obj.a, GoodMSONClass)
         assert obj.a.b == 1
 
+    def test_dataclass(self):
+
+        c = Coordinates([Point(1, 2), Point(3, 4)])
+        d = c.as_dict()
+        c2 = Coordinates.from_dict(d)
+        self.assertEqual(d["points"][0]['x'], 1)
+        self.assertEqual(d["points"][1]['y'], 4)
+        self.assertIsInstance(c2, Coordinates)
+        self.assertIsInstance(c2.points[0], Point)
 
 if __name__ == "__main__":
     unittest.main()