Index: lnt/server/db/rules/rule_update_profile_stats.py
===================================================================
--- lnt/server/db/rules/rule_update_profile_stats.py
+++ lnt/server/db/rules/rule_update_profile_stats.py
@@ -20,7 +20,8 @@
         return
 
     try:
-        history = json.loads(open(history_path).read())
+        with open(history_path) as f:
+            history = json.loads(f.read())
     except Exception:
         history = []
     age = []
@@ -38,8 +39,10 @@
         sz = os.stat(f).st_size // 1000
         age.append([mtime, sz])
 
-    open(history_path, 'w').write(json.dumps(history))
-    open(age_path, 'w').write(json.dumps(age))
+    with open(history_path, 'w') as history_f:
+        history_f.write(json.dumps(history))
+    with open(age_path, 'w') as age_f:
+        age_f.write(json.dumps(age))
 
 
 post_submission_hook = update_profile_stats
Index: lnt/server/instance.py
===================================================================
--- lnt/server/instance.py
+++ lnt/server/instance.py
@@ -54,7 +54,8 @@
             raise Exception("Invalid config: %r" % config_path)
 
         config_data = {}
-        exec(open(config_path).read(), config_data)
+        with open(config_path) as f:
+            exec(f.read(), config_data)
         config = lnt.server.config.Config.from_data(config_path, config_data)
 
         return Instance(config_path, config, tmpdir)
Index: lnt/testing/profile/perf.py
===================================================================
--- lnt/testing/profile/perf.py
+++ lnt/testing/profile/perf.py
@@ -18,7 +18,8 @@
 
     @staticmethod
     def checkFile(fn):
-        return open(fn, 'rb').read(8) == b'PERFILE2'
+        with open(fn, 'rb') as f:
+            return f.read(8) == b'PERFILE2'
 
     @staticmethod
     def deserialize(f, nm='nm', objdump='objdump', propagateExceptions=False):
Index: lnt/testing/profile/profilev1impl.py
===================================================================
--- lnt/testing/profile/profilev1impl.py
+++ lnt/testing/profile/profilev1impl.py
@@ -45,7 +45,8 @@
     @staticmethod
     def checkFile(fn):
         # "zlib compressed data" - 78 9C
-        return open(fn, 'rb').read(2) == b'\x78\x9c'
+        with open(fn, 'rb') as f:
+            return f.read(2) == b'\x78\x9c'
 
     @staticmethod
     def deserialize(fobj):
Index: lnt/testing/profile/profilev2impl.py
===================================================================
--- lnt/testing/profile/profilev2impl.py
+++ lnt/testing/profile/profilev2impl.py
@@ -560,7 +560,8 @@
     def checkFile(fn):
         # The first number is the version (2); ULEB encoded this is simply
         # 0x02.
-        return open(fn, 'rb').read(1) == b'\x02'
+        with open(fn, 'rb') as f:
+            return f.read(1) == b'\x02'
 
     @staticmethod
     def deserialize(fobj):
Index: lnt/testing/util/compilers.py
===================================================================
--- lnt/testing/util/compilers.py
+++ lnt/testing/util/compilers.py
@@ -186,7 +186,8 @@
                          (cc, cc_target_assembly))
 
     cc_exec_hash = hashlib.sha1()
-    cc_exec_hash.update(open(cc, 'rb').read())
+    with open(cc, 'rb') as f:
+        cc_exec_hash.update(f.read())
 
     info = {
         'cc_build': cc_build,
Index: lnt/tests/test_suite.py
===================================================================
--- lnt/tests/test_suite.py
+++ lnt/tests/test_suite.py
@@ -639,7 +639,8 @@
             # failures!
             pass
         try:
-            return json.loads(open(output_json_path.name).read())
+            with open(output_json_path.name) as f:
+                return json.loads(f.read())
         except ValueError as e:
             fatal("Running test-suite did not create valid json report "
                   "in {}: {}".format(output_json_path.name, e))