diff --git a/models/base_model.py b/models/base_model.py
index e4bba811..eacb1231 100755
--- a/models/base_model.py
+++ b/models/base_model.py
@@ -57,7 +57,7 @@ def load_network(self, network, network_label, epoch_label, save_dir=''):
         if not os.path.isfile(save_path):
             print('%s not exists yet!' % save_path)
             if network_label == 'G':
-                raise('Generator must exist!')
+                raise NotImplementedError('Generator must exist!')
         else:
             #network.load_state_dict(torch.load(save_path))
             try:
@@ -76,7 +76,7 @@ def load_network(self, network, network_label, epoch_label, save_dir=''):
                         if v.size() == model_dict[k].size():
                             model_dict[k] = v
 
-                    if sys.version_info >= (3,0):
+                    if sys.version_info >= (2, 6):
                         not_initialized = set()
                     else:
                         from sets import Set
diff --git a/models/networks.py b/models/networks.py
index 476ccb3d..4e11c26e 100755
--- a/models/networks.py
+++ b/models/networks.py
@@ -37,7 +37,7 @@ def define_G(input_nc, output_nc, ngf, netG, n_downsample_global=3, n_blocks_glo
     elif netG == 'encoder':
         netG = Encoder(input_nc, output_nc, ngf, n_downsample_global, norm_layer)
     else:
-        raise('generator not implemented!')
+        raise NotImplementedError('generator [%s] not implemented!' % netG)
     print(netG)
     if len(gpu_ids) > 0:
         assert(torch.cuda.is_available())   
diff --git a/models/pix2pixHD_model.py b/models/pix2pixHD_model.py
index 851460e1..1bfa30d9 100755
--- a/models/pix2pixHD_model.py
+++ b/models/pix2pixHD_model.py
@@ -86,7 +86,7 @@ def initialize(self, opt):
             # optimizer G
             if opt.niter_fix_global > 0:                
                 import sys
-                if sys.version_info >= (3,0):
+                if sys.version_info >= (2, 6):
                     finetune_list = set()
                 else:
                     from sets import Set
diff --git a/models/ui_model.py b/models/ui_model.py
index 056a335d..e7c42d93 100755
--- a/models/ui_model.py
+++ b/models/ui_model.py
@@ -4,7 +4,6 @@
 from torch.autograd import Variable
 from collections import OrderedDict
 import numpy as np
-import os
 from PIL import Image
 import util.util as util
 from .base_model import BaseModel
diff --git a/run_engine.py b/run_engine.py
index 700494d2..bf1c180e 100644
--- a/run_engine.py
+++ b/run_engine.py
@@ -1,8 +1,6 @@
 import os
 import sys
-from random import randint
 import numpy as np
-import tensorrt
 
 try:
     from PIL import Image
diff --git a/util/visualizer.py b/util/visualizer.py
index 41a43c08..dd80a905 100755
--- a/util/visualizer.py
+++ b/util/visualizer.py
@@ -1,6 +1,5 @@
 ### Copyright (C) 2017 NVIDIA Corporation. All rights reserved.
 ### Licensed under the CC BY-NC-SA 4.0 license (https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode).
-import numpy as np
 import os
 import ntpath
 import time