fixed linter issues (cvat-ai#1538)

Author: azhavoro

cvat/apps/dataset_manager/views.py

@@ -30,7 +30,11 @@ def log_exception(logger=None, exc_info=True):
 
 
 def get_export_cache_dir(db_task):
-    return osp.join(db_task.get_task_dirname(), 'export_cache')
+    task_dir = osp.abspath(db_task.get_task_dirname())
+    if osp.isdir(task_dir):
+        return osp.join(task_dir, 'export_cache')
+    else:
+        raise Exception('Task dir {} does not exist'.format(task_dir))
 
 DEFAULT_CACHE_TTL = timedelta(hours=10)
 CACHE_TTL = DEFAULT_CACHE_TTL

cvat/apps/engine/tests/_test_rest_api.py

@@ -1458,8 +1458,9 @@ def test_api_v1_tasks_no_auth(self):
 
 def generate_image_file(filename):
     f = BytesIO()
-    width = random.randint(100, 800)
-    height = random.randint(100, 800)
+    gen = random.SystemRandom()
+    width = gen.randint(100, 800)
+    height = gen.randint(100, 800)
     image = Image.new('RGB', size=(width, height))
     image.save(f, 'jpeg')
     f.name = filename