fix: Make lambda compatiable with python3.

Author: abawchen

graphene_mongo/fields.py

@@ -67,7 +67,7 @@ def args(self, args):
     @property
     def default_filter_args(self):
         return reduce(
-            lambda r, (k, v): r.update({k: v._type._of_type()}) or r if hasattr(v, '_type') else r,
+            lambda r, kv: r.update({kv[0]: kv[1]._type._of_type()}) or r if hasattr(kv[1], '_type') else r,
             self.fields.items(),
             {}
         )

graphene_mongo/utils.py

@@ -31,15 +31,6 @@ def maybe_queryset(value):
     return value
 
 
-def get_default_filter_fields(node):
-    # Notes: Convert all model fields into filter fields by default,
-    #        except for Dynamic type.
-    return reduce(
-        lambda r, (k, v): r.update({k, v._type._of_type()}) or r if hasattr(v, '_type') else a,
-        node._meta.fields.items(),
-        {}
-    )
-
 def import_single_dispatch():
     try:
         from functools import singledispatch