From 253983559b91e2f4bdad4d2eaf6525da93dcbc7f Mon Sep 17 00:00:00 2001
From: Spencer Ellinor <zpencerq@users.noreply.github.com>
Date: Mon, 30 Sep 2019 06:30:14 -0700
Subject: [PATCH] Support use of TypeVar on generic subclasses (#842)

* Add failing generic subclass test

* Only raise type parameter failure on base GenericModel class

* Add changes to describe PR #842

* Change the class check to use is

* Fix formatting in subclass test

* correct change
---
 changes/842-zpencerq.rst |  1 +
 pydantic/generics.py     |  2 +-
 tests/test_generics.py   | 10 ++++++++++
 3 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 changes/842-zpencerq.rst

diff --git a/changes/842-zpencerq.rst b/changes/842-zpencerq.rst
new file mode 100644
index 0000000..fcd1b34
--- /dev/null
+++ b/changes/842-zpencerq.rst
@@ -0,0 +1 @@
+Only check ``TypeVar`` param on base ``GenericModel`` class
diff --git a/pydantic/generics.py b/pydantic/generics.py
index ab3ea52..9380a28 100644
--- a/pydantic/generics.py
+++ b/pydantic/generics.py
@@ -27,7 +27,7 @@ class GenericModel(BaseModel):
             raise TypeError('Cannot parameterize a concrete instantiation of a generic model')
         if not isinstance(params, tuple):
             params = (params,)
-        if any(isinstance(param, TypeVar) for param in params):  # type: ignore
+        if cls is GenericModel and any(isinstance(param, TypeVar) for param in params):  # type: ignore
             raise TypeError(f'Type parameters should be placed on typing.Generic, not GenericModel')
         if Generic not in cls.__bases__:
             raise TypeError(f'Type {cls.__name__} must inherit from typing.Generic before being parameterized')
diff --git a/tests/test_generics.py b/tests/test_generics.py
index 4de02c8..8b13feb 100644
--- a/tests/test_generics.py
+++ b/tests/test_generics.py
@@ -174,6 +174,16 @@ def test_parameters_must_be_typevar():
     assert str(exc_info.value) == f'Type parameters should be placed on typing.Generic, not GenericModel'
 
 
+@skip_36
+def test_subclass_can_be_genericized():
+    T = TypeVar('T')
+
+    class Result(GenericModel, Generic[T]):
+        pass
+
+    Result[T]
+
+
 @skip_36
 def test_parameter_count():
     T = TypeVar('T')