Updating imports to work when singledispatch is available natively

Author: adamcharnock

graphene/contrib/django/converter.py

@@ -1,8 +1,10 @@
 from django.db import models
-from singledispatch import singledispatch
 
+from .utils import import_single_dispatch
 from ...core.types.scalars import ID, Boolean, Float, Int, String
 
+singledispatch = import_single_dispatch()
+
 try:
     UUIDField = models.UUIDField
 except AttributeError:

graphene/contrib/django/filter/__init__.py

@@ -1,3 +1,11 @@
+try:
+    import django_filters
+except:
+    raise Exception(
+        "Use of django filtering requires the django-filter package "
+        "be installed. You can do so using `pip install django-filter`"
+    )
+
 from .fields import DjangoFilterConnectionField
 from .filterset import GrapheneFilterSet, GlobalIDFilter, GlobalIDMultipleChoiceFilter
 from .resolvers import FilterConnectionResolver

graphene/contrib/django/form_converter.py

@@ -1,10 +1,10 @@
 from django import forms
 from django.forms.fields import BaseTemporalField
-from singledispatch import singledispatch
-
 from graphene import String, Int, Boolean, Float, ID
 from graphene.contrib.django.forms import GlobalIDFormField, GlobalIDMultipleChoiceField
+from graphene.contrib.django.utils import import_single_dispatch
 from graphene.core.types.definitions import List
+singledispatch = import_single_dispatch()
 
 try:
     UUIDField = forms.UUIDField

graphene/contrib/django/utils.py

@@ -3,7 +3,6 @@
 from django.db.models.manager import Manager
 
 from graphene import Argument, String
-from graphene.contrib.django.form_converter import convert_form_field
 
 
 def get_type_for_model(schema, model):
@@ -36,6 +35,8 @@ def get_filtering_args_from_filterset(filterset_class, type):
         a Graphene Field. These arguments will be available to
         filter against in the GraphQL
     """
+    from graphene.contrib.django.form_converter import convert_form_field
+
     args = {}
     for name, filter_field in six.iteritems(filterset_class.base_filters):
         field_type = Argument(convert_form_field(filter_field.field))
@@ -46,3 +47,26 @@ def get_filtering_args_from_filterset(filterset_class, type):
     # Also add the 'order_by' field
     args[filterset_class.order_by_field] = Argument(String)
     return args
+
+
+def import_single_dispatch():
+    singledispatch = None
+    try:
+        from functools import singledispatch
+    except ImportError:
+        pass
+
+    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