If using Python >=3.7, use built-in dict as OrderedDict (graphql-pyth…

…on#248)

If using Python >=3.7, use built-in dict as OrderedDict

Since dictionaries are specified to preserve insertion order in
Python 3.7 and up (see https://docs.python.org/3/whatsnew/3.7.html),
it seems simplest and most performant to use the built-in type
where possible.

graphql/pyutils/ordereddict.py

@@ -1,8 +1,16 @@
-try:
-    # Try to load the Cython performant OrderedDict (C)
-    # as is more performant than collections.OrderedDict (Python)
-    from cyordereddict import OrderedDict  # type: ignore
-except ImportError:
-    from collections import OrderedDict
+import sys
+
+if sys.version_info >= (3, 7):
+    # As of Python 3.7, dictionaries are specified to preserve insertion order
+    OrderedDict = dict
+
+else:
+    try:
+        # Try to load the Cython performant OrderedDict (C)
+        # as is more performant than collections.OrderedDict (Python)
+        from cyordereddict import OrderedDict  # type: ignore
+    except ImportError:
+        from collections import OrderedDict
+
 
 __all__ = ["OrderedDict"]

graphql/type/definition.py

@@ -404,6 +404,7 @@ def __init__(
     @cached_property
     def fields(self):
         # type: () -> Dict[str, GraphQLField]
+        assert self._fields is not None, '"fields" cannot be None'
         return define_field_map(self, self._fields)
 
 

graphql/type/tests/test_enum_type.py

@@ -1,3 +1,4 @@
+import sys
 from collections import OrderedDict
 from rx import Observable
 from graphql import graphql
@@ -11,6 +12,7 @@
     GraphQLSchema,
     GraphQLString,
 )
+import pytest
 
 ColorType = GraphQLEnumType(
     name="Color",
@@ -263,6 +265,10 @@ def test_presents_a_get_value_api():
     assert badUsage is None
 
 
+@pytest.mark.skipif(
+    sys.version_info >= (3, 7),
+    reason="As of Python 3.7 we use built-in dicts, which preserve order",
+)
 def test_sorts_values_if_not_using_ordered_dict():
     enum = GraphQLEnumType(
         name="Test",