Subclass abcmeta (#123)

* Added compatibility with python's ABC

* Added documentation

* Added link

HISTORY.rst

@@ -3,6 +3,10 @@
 History
 -------
 
+v0.6.5 (2018-02-XX)
+...................
+* added compatibility with abstract base classes (ABCs) #123
+
 v0.6.4 (2018-02-01)
 ...................
 * allow python date and times objects #122

docs/examples/ex_abc.py

@@ -0,0 +1,11 @@
+import abc
+from pydantic import BaseModel
+
+
+class FooBarModel(BaseModel, abc.ABC):
+    a: str
+    b: int
+
+    @abc.abstractmethod
+    def my_abstract_method(self):
+        pass

docs/index.rst

@@ -335,6 +335,14 @@ Using the same plumbing as ``copy()`` pydantic models support efficient pickling
 
 .. literalinclude:: examples/ex_pickle.py
 
+Abstract Base Classes
+.....................
+
+Pydantic models can be used alongside Python's
+`Abstract Base Classes <https://docs.python.org/3/library/abc.html>`_ (ABCs).
+
+.. literalinclude:: examples/ex_abc.py
+
 .. _benchmarks_tag:
 
 Benchmarks

pydantic/main.py

@@ -1,4 +1,5 @@
 import warnings
+from abc import ABCMeta
 from collections import OrderedDict
 from pathlib import Path
 from types import FunctionType
@@ -51,7 +52,7 @@ def _extract_validators(namespace):
     return validators
 
 
-class MetaModel(type):
+class MetaModel(ABCMeta):
     @classmethod
     def __prepare__(mcs, *args, **kwargs):
         return OrderedDict()

tests/test_abc.py

@@ -0,0 +1,44 @@
+import abc
+
+import pytest
+
+from pydantic import BaseModel
+
+
+def test_model_subclassing_abstract_base_classes():
+    class Model(BaseModel, abc.ABC):
+        some_field: str
+
+
+def test_model_subclassing_abstract_base_classes_without_implementation_raises_exception():
+    class Model(BaseModel, abc.ABC):
+        some_field: str
+
+        @abc.abstractmethod
+        def my_abstract_method(self):
+            pass
+
+        @classmethod
+        @abc.abstractmethod
+        def my_abstract_classmethod(cls):
+            pass
+
+        @staticmethod
+        @abc.abstractmethod
+        def my_abstract_staticmethod():
+            pass
+
+        @property
+        @abc.abstractmethod
+        def my_abstract_property(self):
+            pass
+
+        @my_abstract_property.setter
+        @abc.abstractmethod
+        def my_abstract_property(self, val):
+            pass
+
+    with pytest.raises(TypeError) as excinfo:
+        Model(some_field='some_value')
+    assert str(excinfo.value) == "Can't instantiate abstract class Model with abstract methods" \
+        " my_abstract_classmethod, my_abstract_method, my_abstract_property, my_abstract_staticmethod"