diff --git a/tools/cwrap.py b/tools/cwrap.py
index 912423e7..d19caee3 100644
--- a/tools/cwrap.py
+++ b/tools/cwrap.py
@@ -11,51 +11,63 @@
 concore.delay = 0.02
 
 try:
-    apikey=open(concore.inpath+'1/concore.apikey',newline=None).readline().rstrip()
+    with open(concore.inpath+'1/concore.apikey',newline=None) as f:
+        apikey=f.readline().rstrip()
 except (OSError, IOError):
     try: 
         #perhaps this should be removed for security
-        apikey=open('./concore.apikey',newline=None).readline().rstrip()
+        with open('./concore.apikey',newline=None) as f:
+            apikey=f.readline().rstrip()
     except (OSError, IOError):
         apikey = ''
 
 try:
-    yuyu=open(concore.inpath+'1/concore.yuyu',newline=None).readline().rstrip()
+    with open(concore.inpath+'1/concore.yuyu',newline=None) as f:
+        yuyu=f.readline().rstrip()
 except (OSError, IOError):
     try: 
-        yuyu=open('./concore.yuyu',newline=None).readline().rstrip()
+        with open('./concore.yuyu',newline=None) as f:
+            yuyu=f.readline().rstrip()
     except (OSError, IOError):
         yuyu = 'yuyu'
 
 try:
-    name1=open(concore.inpath+'1/concore.name1',newline=None).readline().rstrip()
+    with open(concore.inpath+'1/concore.name1',newline=None) as f:
+        name1=f.readline().rstrip()
 except (OSError, IOError):
     try:
-        name1=open('./concore.name1',newline=None).readline().rstrip()
+        with open('./concore.name1',newline=None) as f:
+            name1=f.readline().rstrip()
     except (OSError, IOError):
         name1 = 'u'
 
 try:
-    name2=open(concore.inpath+'1/concore.name2',newline=None).readline().rstrip()
+    with open(concore.inpath+'1/concore.name2',newline=None) as f:
+        name2=f.readline().rstrip()
 except (OSError, IOError):
     try:
-        name2=open('./concore.name2',newline=None).readline().rstrip()
+        with open('./concore.name2',newline=None) as f:
+            name2=f.readline().rstrip()
     except (OSError, IOError):
         name2 = 'ym'
 
 try:
-    init_simtime_u = open(concore.inpath+'1/concore.init1',newline=None).readline().rstrip()
+    with open(concore.inpath+'1/concore.init1',newline=None) as f:
+        init_simtime_u = f.readline().rstrip()
 except (OSError, IOError):
     try:
-        init_simtime_u = open('./concore.init1',newline=None).readline().rstrip()
+        with open('./concore.init1',newline=None) as f:
+            init_simtime_u = f.readline().rstrip()
     except (OSError, IOError):
         init_simtime_u = "[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]"
 
 try:
-    init_simtime_ym = open(concore.inpath+'1/concore.init2',newline=None).readline().rstrip()
+    with open(concore.inpath+'1/concore.init2',newline=None) as f:
+        init_simtime_ym = f.readline().rstrip()
 except (OSError, IOError):
     try:
-        init_simtime_ym = open('./concore.init2',newline=None).readline().rstrip()
+        with open('./concore.init2',newline=None) as f:
+            init_simtime_ym = f.readline().rstrip()
     except (OSError, IOError):
         init_simtime_ym = "[0.0, 0.0, 0.0]"
 
@@ -82,10 +94,11 @@
     logging.debug("CW outer loop")
     while concore.unchanged():
         u = concore.read(1,name1,init_simtime_u)
-    f = {'file1': open(concore.inpath+'1/'+name1, 'rb')}
-    logging.debug(f"CW: before post u={u}")
-    logging.debug(f'http://www.controlcore.org/pm/{yuyu}{apikey}&fetch={name2}')
-    r = requests.post('http://www.controlcore.org/pm/'+yuyu+apikey+'&fetch='+name2, files=f,timeout=timeout_max)
+    with open(concore.inpath+'1/'+name1, 'rb') as f1:
+        f = {'file1': f1}
+        logging.debug(f"CW: before post u={u}")
+        logging.debug(f'http://www.controlcore.org/pm/{yuyu}{apikey}&fetch={name2}')
+        r = requests.post('http://www.controlcore.org/pm/'+yuyu+apikey+'&fetch='+name2, files=f,timeout=timeout_max)
     if r.status_code!=200:
         logging.error(f"bad POST request {r.status_code}")
         quit()
@@ -101,11 +114,12 @@
     while oldt==t or len(r.content)==0:
         time.sleep(concore.delay)
         logging.debug(f"CW waiting status={r.status_code} content={r.content.decode('utf-8')} t={t}")
-        f = {'file1': open(concore.inpath+'1/'+name1, 'rb')}
-        try:
-            r = requests.post('http://www.controlcore.org/pm/'+yuyu+apikey+'&fetch='+name2, files=f,timeout=timeout_max)
-        except Exception:
-            logging.error("CW: bad request")
+        with open(concore.inpath+'1/'+name1, 'rb') as f1:
+            f = {'file1': f1}
+            try:
+                r = requests.post('http://www.controlcore.org/pm/'+yuyu+apikey+'&fetch='+name2, files=f,timeout=timeout_max)
+            except Exception:
+                logging.error("CW: bad request")
         timeout_count += 1
         if r.status_code!=200 or time.perf_counter()-t1 > 1.1*timeout_max: #timeout_count>100:
             logging.error(f"timeout or bad POST request {r.status_code}")