diff --git a/stun/__init__.py b/stun/__init__.py
index c7aef24..ec24be7 100644
--- a/stun/__init__.py
+++ b/stun/__init__.py
@@ -86,22 +86,19 @@
 SymmetricNAT = "Symmetric NAT"
 ChangedAddressError = "Meet an error, when do Test1 on Changed IP and Port"
 
+def b2a_hexstr(abytes):
+    return binascii.b2a_hex(abytes).decode("ascii")
 
 def _initialize():
-    items = dictAttrToVal.items()
-    for i in range(len(items)):
-        dictValToAttr.update({items[i][1]: items[i][0]})
-    items = dictMsgTypeToVal.items()
-    for i in range(len(items)):
-        dictValToMsgType.update({items[i][1]: items[i][0]})
-
+    global dictValToAttr, dictValToMsgType
+    dictValToAttr= {v: k for k, v in dictAttrToVal.items()}
+    dictValToMsgType = {v: k for k, v in dictMsgTypeToVal.items()}
 
 def gen_tran_id():
     a = ''.join(random.choice('0123456789ABCDEF') for i in range(32))
     # return binascii.a2b_hex(a)
     return a
 
-
 def stun_test(sock, host, port, source_ip, source_port, send_data=""):
     retVal = {'Resp': False, 'ExternalIP': None, 'ExternalPort': None,
               'SourceIP': None, 'SourcePort': None, 'ChangedIP': None,
@@ -132,45 +129,45 @@ def stun_test(sock, host, port, source_ip, source_port, send_data=""):
                 else:
                     retVal['Resp'] = False
                     return retVal
-        msgtype = binascii.b2a_hex(buf[0:2])
+        msgtype = b2a_hexstr(buf[0:2])
         bind_resp_msg = dictValToMsgType[msgtype] == "BindResponseMsg"
-        tranid_match = tranid.upper() == binascii.b2a_hex(buf[4:20]).upper()
+        tranid_match = tranid.upper() == b2a_hexstr(buf[4:20]).upper()
         if bind_resp_msg and tranid_match:
             recvCorr = True
             retVal['Resp'] = True
-            len_message = int(binascii.b2a_hex(buf[2:4]), 16)
+            len_message = int(b2a_hexstr(buf[2:4]), 16)
             len_remain = len_message
             base = 20
             while len_remain:
-                attr_type = binascii.b2a_hex(buf[base:(base + 2)])
-                attr_len = int(binascii.b2a_hex(buf[(base + 2):(base + 4)]), 16)
+                attr_type = b2a_hexstr(buf[base:(base + 2)])
+                attr_len = int(b2a_hexstr(buf[(base + 2):(base + 4)]), 16)
                 if attr_type == MappedAddress:
-                    port = int(binascii.b2a_hex(buf[base + 6:base + 8]), 16)
+                    port = int(b2a_hexstr(buf[base + 6:base + 8]), 16)
                     ip = ".".join([
-                        str(int(binascii.b2a_hex(buf[base + 8:base + 9]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 9:base + 10]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 10:base + 11]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 11:base + 12]), 16))
+                        str(int(b2a_hexstr(buf[base + 8:base + 9]), 16)),
+                        str(int(b2a_hexstr(buf[base + 9:base + 10]), 16)),
+                        str(int(b2a_hexstr(buf[base + 10:base + 11]), 16)),
+                        str(int(b2a_hexstr(buf[base + 11:base + 12]), 16))
                     ])
                     retVal['ExternalIP'] = ip
                     retVal['ExternalPort'] = port
                 if attr_type == SourceAddress:
-                    port = int(binascii.b2a_hex(buf[base + 6:base + 8]), 16)
+                    port = int(b2a_hexstr(buf[base + 6:base + 8]), 16)
                     ip = ".".join([
-                        str(int(binascii.b2a_hex(buf[base + 8:base + 9]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 9:base + 10]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 10:base + 11]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 11:base + 12]), 16))
+                        str(int(b2a_hexstr(buf[base + 8:base + 9]), 16)),
+                        str(int(b2a_hexstr(buf[base + 9:base + 10]), 16)),
+                        str(int(b2a_hexstr(buf[base + 10:base + 11]), 16)),
+                        str(int(b2a_hexstr(buf[base + 11:base + 12]), 16))
                     ])
                     retVal['SourceIP'] = ip
                     retVal['SourcePort'] = port
                 if attr_type == ChangedAddress:
-                    port = int(binascii.b2a_hex(buf[base + 6:base + 8]), 16)
+                    port = int(b2a_hexstr(buf[base + 6:base + 8]), 16)
                     ip = ".".join([
-                        str(int(binascii.b2a_hex(buf[base + 8:base + 9]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 9:base + 10]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 10:base + 11]), 16)),
-                        str(int(binascii.b2a_hex(buf[base + 11:base + 12]), 16))
+                        str(int(b2a_hexstr(buf[base + 8:base + 9]), 16)),
+                        str(int(b2a_hexstr(buf[base + 9:base + 10]), 16)),
+                        str(int(b2a_hexstr(buf[base + 10:base + 11]), 16)),
+                        str(int(b2a_hexstr(buf[base + 11:base + 12]), 16))
                     ])
                     retVal['ChangedIP'] = ip
                     retVal['ChangedPort'] = port
diff --git a/stun/cli.py b/stun/cli.py
index 543a92d..a166ce9 100644
--- a/stun/cli.py
+++ b/stun/cli.py
@@ -57,6 +57,7 @@ def main():
         print('NAT Type:', nat_type)
         print('External IP:', external_ip)
         print('External Port:', external_port)
+        input('Press any key to continue')
     except KeyboardInterrupt:
         sys.exit()