Remove singledispatch dependency

singledispatch is inluded with Python >= 3.4, no need for external
package.

graphene_django/converter.py

@@ -1,4 +1,6 @@
 from collections import OrderedDict
+from functools import singledispatch
+
 from django.db import models
 from django.utils.encoding import force_str
 from django.utils.module_loading import import_string
@@ -26,9 +28,6 @@ from graphql import assert_valid_name
 from .settings import graphene_settings
 from .compat import ArrayField, HStoreField, JSONField, RangeField
 from .fields import DjangoListField, DjangoConnectionField
-from .utils import import_single_dispatch
-
-singledispatch = import_single_dispatch()
 
 
 def convert_choice_name(name):

graphene_django/forms/converter.py

@@ -1,13 +1,11 @@
+from functools import singledispatch
+
 from django import forms
 from django.core.exceptions import ImproperlyConfigured
 
 from graphene import ID, Boolean, Float, Int, List, String, UUID, Date, DateTime, Time
 
 from .forms import GlobalIDFormField, GlobalIDMultipleChoiceField
-from ..utils import import_single_dispatch
-
-
-singledispatch = import_single_dispatch()
 
 
 @singledispatch

graphene_django/rest_framework/serializer_converter.py

@@ -1,3 +1,5 @@
+from functools import singledispatch
+
 from django.core.exceptions import ImproperlyConfigured
 from rest_framework import serializers
 
@@ -5,11 +7,8 @@ import graphene
 
 from ..registry import get_global_registry
 from ..converter import convert_choices_to_named_enum_with_descriptions
-from ..utils import import_single_dispatch
 from .types import DictType
 
-singledispatch = import_single_dispatch()
-
 
 @singledispatch
 def get_graphene_type_from_serializer_field(field):

graphene_django/utils/__init__.py

@@ -4,7 +4,6 @@ from .utils import (
     camelize,
     get_model_fields,
     get_reverse_fields,
-    import_single_dispatch,
     is_valid_django_model,
     maybe_queryset,
 )
@@ -16,6 +15,5 @@ __all__ = [
     "get_model_fields",
     "camelize",
     "is_valid_django_model",
-    "import_single_dispatch",
     "GraphQLTestCase",
 ]

graphene_django/utils/utils.py

@@ -76,26 +76,3 @@ def get_model_fields(model):
 
 def is_valid_django_model(model):
     return inspect.isclass(model) and issubclass(model, models.Model)
-
-
-def import_single_dispatch():
-    try:
-        from functools import singledispatch
-    except ImportError:
-        singledispatch = None
-
-    if not singledispatch:
-        try:
-            from singledispatch import singledispatch
-        except ImportError:
-            pass
-
-    if not singledispatch:
-        raise Exception(
-            "It seems your python version does not include "
-            "functools.singledispatch. Please install the 'singledispatch' "
-            "package. More information here: "
-            "https://pypi.python.org/pypi/singledispatch"
-        )
-
-    return singledispatch

setup.py

@@ -55,7 +55,6 @@ setup(
         "graphene>=2.1.7,<3",
         "graphql-core>=2.1.0,<3",
         "Django>=1.11,!=2.0.*,!=2.1.*",
-        "singledispatch>=3.4.0.3",
         "promise>=2.1",
     ],
     setup_requires=["pytest-runner"],