diff --git a/account/decorators.py b/account/decorators.py
index e424e8c4..5497565a 100644
--- a/account/decorators.py
+++ b/account/decorators.py
@@ -4,7 +4,7 @@ from utils.api import JSONResponse
 
 from .models import ProblemPermission
 
-from contest.models import Contest, ContestType, ContestStatus
+from contest.models import Contest, ContestType
 
 
 class BasePermissionDecorator(object):
@@ -67,10 +67,10 @@ def check_contest_permission(func):
         self = args[0]
         request = args[1]
         user = request.user
-        if kwargs.get('contest_id'):
-            contest_id = kwargs.pop('contest_id')
+        if kwargs.get("contest_id"):
+            contest_id = kwargs.pop("contest_id")
         else:
-            contest_id = request.GET.get('contest_id')
+            contest_id = request.GET.get("contest_id")
         if not contest_id:
             return self.error("Parameter contest_id not exist.")
 
diff --git a/contest/serializers.py b/contest/serializers.py
index 3e842fb1..8fb4beee 100644
--- a/contest/serializers.py
+++ b/contest/serializers.py
@@ -2,8 +2,6 @@ from utils.api import DateTimeTZField, UsernameSerializer, serializers
 
 from .models import Contest, ContestAnnouncement, ContestRuleType
 
-from problem.serializers import ContestProblemSerializer
-
 
 class CreateConetestSeriaizer(serializers.Serializer):
     title = serializers.CharField(max_length=128)
@@ -43,7 +41,7 @@ class ContestAdminSerializer(serializers.ModelSerializer):
 class ContestSerializer(ContestAdminSerializer):
     class Meta:
         model = Contest
-        exclude = ('password', 'visible')
+        exclude = ("password", "visible")
 
 
 class ContestAnnouncementSerializer(serializers.ModelSerializer):
diff --git a/problem/serializers.py b/problem/serializers.py
index ad391c19..fff369d9 100644
--- a/problem/serializers.py
+++ b/problem/serializers.py
@@ -99,4 +99,4 @@ class ContestProblemSerializer(serializers.ModelSerializer):
     created_by = UsernameSerializer()
 
     class Meta:
-        model = ContestProblem
\ No newline at end of file
+        model = ContestProblem
diff --git a/problem/tests.py b/problem/tests.py
index 34e0f496..3bdc79c9 100644
--- a/problem/tests.py
+++ b/problem/tests.py
@@ -208,18 +208,17 @@ class ContestProblemTest(APITestCase):
     def test_get_one_contest_problem(self):
         contest_id = self.contest.data["data"]["id"]
         problem_id = self.problem.data["data"]["_id"]
-        resp = self.client.get("{}?contest_id={}&problem_id={}".format(self.url,contest_id, problem_id))
+        resp = self.client.get("{}?contest_id={}&problem_id={}".format(self.url, contest_id, problem_id))
         self.assertSuccess(resp)
 
     def test_regular_user_get_contest_problem(self):
         self.create_user("test", "test123")
         contest_id = self.contest.data["data"]["id"]
         problem_id = self.problem.data["data"]["_id"]
-        resp = self.client.get("{}?contest_id={}&problem_id={}".format(self.url,contest_id, problem_id))
+        resp = self.client.get("{}?contest_id={}&problem_id={}".format(self.url, contest_id, problem_id))
         self.assertFailed(resp)
 
         url = self.reverse("contest_password_api")
         self.client.post(url, {"contest_id": contest_id, "password": DEFAULT_CONTEST_DATA["password"]})
-        resp = self.client.get("{}?contest_id={}&problem_id={}".format(self.url,contest_id, problem_id))
+        resp = self.client.get("{}?contest_id={}&problem_id={}".format(self.url, contest_id, problem_id))
         self.assertSuccess(resp)
-    
diff --git a/problem/views/oj.py b/problem/views/oj.py
index c273bddf..8565bec8 100644
--- a/problem/views/oj.py
+++ b/problem/views/oj.py
@@ -1,6 +1,6 @@
 from django.db.models import Q
 from utils.api import APIView
-from account.decorators import login_required, check_contest_permission
+from account.decorators import check_contest_permission
 from ..models import ProblemTag, Problem, ContestProblem
 from ..serializers import ProblemSerializer, TagSerializer
 from ..serializers import ContestProblemSerializer
diff --git a/submission/views/oj.py b/submission/views/oj.py
index 626b8c3b..b9a90070 100644
--- a/submission/views/oj.py
+++ b/submission/views/oj.py
@@ -1,13 +1,12 @@
 from django_redis import get_redis_connection
 
 from account.decorators import login_required
-from account.models import AdminType, User
 from problem.models import Problem, ProblemRuleType
 from submission.tasks import judge_task
 # from judge.dispatcher import JudgeDispatcher
 from utils.api import APIView, validate_serializer
 from utils.throttling import TokenBucket, BucketController
-from ..models import Submission, JudgeStatus
+from ..models import Submission
 from ..serializers import CreateSubmissionSerializer, SubmissionModelSerializer
 from ..serializers import SubmissionSafeSerializer, SubmissionListSerializer
 
@@ -87,5 +86,3 @@ class SubmissionListAPI(APIView):
         data = self.paginate_data(request, subs)
         data["results"] = SubmissionListSerializer(data["results"], many=True, user=request.user).data
         return self.success(data)
-
-