diff --git a/graphql/backend/base.py b/graphql/backend/base.py
index 16dd76b4..36be85bf 100644
--- a/graphql/backend/base.py
+++ b/graphql/backend/base.py
@@ -1,6 +1,7 @@
 from abc import ABCMeta, abstractmethod
-
+from ..pyutils.cached_property import cached_property
 import six
+from ..language import ast
 
 # Necessary for static type checking
 if False:  # flake8: noqa
diff --git a/graphql/language/lexer.py b/graphql/language/lexer.py
index a60bc6e2..a017dbce 100644
--- a/graphql/language/lexer.py
+++ b/graphql/language/lexer.py
@@ -372,7 +372,7 @@ def read_string(source, start):
 
         position += 1
         if code == 92:  # \
-            append(body[chunk_start : position - 1])
+            append(body[chunk_start: position - 1])
 
             code = char_code_at(body, position)
             escaped = ESCAPED_CHAR_CODES.get(code)  # type: ignore
@@ -392,7 +392,7 @@ def read_string(source, start):
                         source,
                         position,
                         u"Invalid character escape sequence: \\u{}.".format(
-                            body[position + 1 : position + 5]
+                            body[position + 1: position + 5]
                         ),
                     )
 
diff --git a/graphql/pyutils/compat.py b/graphql/pyutils/compat.py
index 0012f20b..43613d74 100644
--- a/graphql/pyutils/compat.py
+++ b/graphql/pyutils/compat.py
@@ -240,4 +240,3 @@ def check_threads():
                 '(Enable the "enable-threads" flag).'
             )
         )
-
diff --git a/graphql/type/definition.py b/graphql/type/definition.py
index 9099242e..ce9dffb5 100644
--- a/graphql/type/definition.py
+++ b/graphql/type/definition.py
@@ -626,17 +626,17 @@ class GeoPoint(GraphQLInputObjectType):
     """
 
     def __init__(self,
-            name, # type: str
-            fields, # type: Union[Callable[[], Dict[str, GraphQLInputObjectField]], Dict[str, GraphQLInputObjectField]]
-            description=None, # type: Optional[str]
-            container_type=None, # type: Type[Dict[str, Any]]
-        ):
+            name,  # type: str
+            fields,  # type: Union[Callable[[], Dict[str, GraphQLInputObjectField]], Dict[str, GraphQLInputObjectField]]
+            description=None,  # type: Optional[str]
+            container_type=None,  # type: Type[Dict[str, Any]]
+                 ):
         # type: (...) -> None
         assert name, "Type must be named."
         self.name = name
         self.description = description
         if container_type is None:
-            container_type = dict # type: ignore
+            container_type = dict  # type: ignore
         assert callable(container_type), "container_type must be callable"
         self.container_type = container_type
         self._fields = fields
@@ -755,7 +755,7 @@ class RowType(GraphQLObjectType):
 
     def __init__(
         self,
-        type, # type: Union[GraphQLList, GraphQLObjectType, GraphQLScalarType, GraphQLInputObjectType, GraphQLInterfaceType]
+        type,  # type: Union[GraphQLList, GraphQLObjectType, GraphQLScalarType, GraphQLInputObjectType, GraphQLInterfaceType]
     ):
         # type: (...) -> None
         assert is_type(type) and not isinstance(
diff --git a/graphql/type/tests/test_enum_type.py b/graphql/type/tests/test_enum_type.py
index 6779db9c..989fac82 100644
--- a/graphql/type/tests/test_enum_type.py
+++ b/graphql/type/tests/test_enum_type.py
@@ -1,5 +1,5 @@
 from collections import OrderedDict
-
+from rx import Observable
 from graphql import graphql
 from graphql.type import (
     GraphQLArgument,
diff --git a/graphql/utils/tests/test_build_ast_schema.py b/graphql/utils/tests/test_build_ast_schema.py
index 2080331c..9ac12c2f 100644
--- a/graphql/utils/tests/test_build_ast_schema.py
+++ b/graphql/utils/tests/test_build_ast_schema.py
@@ -1,7 +1,7 @@
 from graphql import GraphQLInt, parse
 from graphql.utils.build_ast_schema import build_ast_schema
 from graphql.utils.schema_printer import print_schema
-
+from pytest import raises
 from ...type import (
     GraphQLDeprecatedDirective,
     GraphQLIncludeDirective,
diff --git a/graphql/validation/rules/overlapping_fields_can_be_merged.py b/graphql/validation/rules/overlapping_fields_can_be_merged.py
index 8506e2cd..4cba7ca2 100644
--- a/graphql/validation/rules/overlapping_fields_can_be_merged.py
+++ b/graphql/validation/rules/overlapping_fields_can_be_merged.py
@@ -207,7 +207,7 @@ def _find_conflicts_within_selection_set(
         # selection set to collect conflicts within fragments spread together.
         # This compares each item in the list of fragment names to every other item
         # in that same list (except for itself).
-        for other_fragment_name in fragment_names[i + 1 :]:
+        for other_fragment_name in fragment_names[i + 1:]:
             _collect_conflicts_between_fragments(
                 context,
                 conflicts,
@@ -444,7 +444,7 @@ def _collect_conflicts_within(
         # (except to itself). If the list only has one item, nothing needs to
         # be compared.
         for i, field in enumerate(fields):
-            for other_field in fields[i + 1 :]:
+            for other_field in fields[i + 1:]:
                 # within one collection is never mutually exclusive
                 conflict = _find_conflict(
                     context,