utc-lize datetime vs time

b.py

import pytz                                                                                          
import datetime                                                                                      
import time                                                                                          
                                                                                                     
s = "2015-01-01 12:34:56"                                                                            
local = pytz.timezone("Asia/Seoul")                                                                  
                                                                                                     
                                                                                                     
begin = datetime.datetime.now()                                                                      
                                                                                                     
for _ in xrange(10000):                                                                              
    naive = datetime.datetime.strptime(s, "%Y-%m-%d %H:%M:%S")                                       
    local_dt = local.localize(naive, is_dst=None)                                                    
    utc = local_dt.astimezone(pytz.utc)                                                              
                                                                                                     
print datetime.datetime.now() - begin                                                                
                                                                                                     
begin = datetime.datetime.now()                                                                      
                                                                                                     
for _ in xrange(10000):                                                                              
    utc = time.gmtime(time.mktime(time.strptime(s, "%Y-%m-%d %H:%M:%S")))                            
                                                                                                     
print datetime.datetime.now() - begin    

0:00:00.474197
0:00:00.204134