diff --git a/css/tools/w3ctestlib/Indexer.py b/css/tools/w3ctestlib/Indexer.py
index 3b71f5bab748ba..f7e2eb2a173182 100644
--- a/css/tools/w3ctestlib/Indexer.py
+++ b/css/tools/w3ctestlib/Indexer.py
@@ -124,9 +124,8 @@ def indexGroup(self, group):
 
   def __writeTemplate(self, template, data, outfile):
     o = self.tt.process(template, data)
-    f = open(outfile, 'w')
-    f.write(o.encode('utf-8'))
-    f.close()
+    with open(outfile, 'w') as f:
+      f.write(o.encode('utf-8'))
 
   def writeOverview(self, destDir, errorOut=sys.stderr, addTests=[]):
     """Write format-agnostic pages such as test suite overview pages,
diff --git a/css/tools/w3ctestlib/Sources.py b/css/tools/w3ctestlib/Sources.py
index 1528cbb8341422..fa704bf6dbc4a2 100644
--- a/css/tools/w3ctestlib/Sources.py
+++ b/css/tools/w3ctestlib/Sources.py
@@ -525,7 +525,8 @@ def relativeURL(self, other):
   def data(self):
     """Return file contents as a byte string."""
     if (self._data is None):
-      self._data = open(self.sourcepath, 'r').read()
+      with open(self.sourcepath, 'r') as f:
+        self._data = f.read()
     if (self._data.startswith(codecs.BOM_UTF8)):
       self.encoding = 'utf-8-sig' # XXX look for other unicode BOMs
     return self._data
@@ -580,8 +581,8 @@ def adjustReferences(source):
   def write(self, format):
     """Writes FileSource.data() out to `self.relpath` through Format `format`."""
     data = self.data()
-    f = open(format.dest(self.relpath), 'w')
-    f.write(data)
+    with open(format.dest(self.relpath), 'w') as f:
+      f.write(data)
     if (self.metaSource):
       self.metaSource.write(format) # XXX need to get output path from format, but not let it choose actual format
 
@@ -818,7 +819,8 @@ def data(self):
     """Merge contents of all config files represented by this source."""
     data = ''
     for src in self.sourcepath:
-      data += open(src).read()
+      with open(src) as f:
+        data += f.read()
       data += '\n'
     return data
 
@@ -868,35 +870,36 @@ def __iter__(self):
     for src in self.sourcepath:
       relbase = basepath(self.relpath)
       srcbase = basepath(src)
-      for line in open(src):
-        strip = self.baseRE.search(line)
-        if strip:
-          striplist.append(strip.group(1))
-        line = self.stripRE.sub('', line)
-        m = self.parseRE.search(line)
-        if m:
-          record = ((join(srcbase, m.group(2)), join(srcbase, m.group(3))), \
-                    (join(relbase, m.group(2)), join(relbase, m.group(3))), \
-                    m.group(1))
-#          for strip in striplist:
-            # strip relrecord
-          if not exists(record[0][0]):
-            raise ReftestFilepathError("Manifest Error in %s: "
-                                       "Reftest test file %s does not exist." \
-                                        % (src, record[0][0]))
-          elif not exists(record[0][1]):
-            raise ReftestFilepathError("Manifest Error in %s: "
-                                       "Reftest reference file %s does not exist." \
-                                       % (src, record[0][1]))
-          elif not isPathInsideBase(record[1][0]):
-            raise ReftestFilepathError("Manifest Error in %s: "
-                                       "Reftest test replath %s not within relpath root." \
-                                       % (src, record[1][0]))
-          elif not isPathInsideBase(record[1][1]):
-            raise ReftestFilepathError("Manifest Error in %s: "
-                                       "Reftest test replath %s not within relpath root." \
-                                       % (src, record[1][1]))
-          yield record
+      with open(src) as f:
+        for line in f:
+          strip = self.baseRE.search(line)
+          if strip:
+            striplist.append(strip.group(1))
+          line = self.stripRE.sub('', line)
+          m = self.parseRE.search(line)
+          if m:
+            record = ((join(srcbase, m.group(2)), join(srcbase, m.group(3))), \
+                      (join(relbase, m.group(2)), join(relbase, m.group(3))), \
+                      m.group(1))
+  #          for strip in striplist:
+              # strip relrecord
+            if not exists(record[0][0]):
+              raise ReftestFilepathError("Manifest Error in %s: "
+                                         "Reftest test file %s does not exist." \
+                                          % (src, record[0][0]))
+            elif not exists(record[0][1]):
+              raise ReftestFilepathError("Manifest Error in %s: "
+                                         "Reftest reference file %s does not exist." \
+                                         % (src, record[0][1]))
+            elif not isPathInsideBase(record[1][0]):
+              raise ReftestFilepathError("Manifest Error in %s: "
+                                         "Reftest test replath %s not within relpath root." \
+                                         % (src, record[1][0]))
+            elif not isPathInsideBase(record[1][1]):
+              raise ReftestFilepathError("Manifest Error in %s: "
+                                         "Reftest test replath %s not within relpath root." \
+                                         % (src, record[1][1]))
+            yield record
 
 import Utils # set up XML catalog
 xhtmlns = '{http://www.w3.org/1999/xhtml}'
@@ -1026,9 +1029,8 @@ def write(self, format, output=None):
       output = self.unicode()
 
     # write
-    f = open(format.dest(self.relpath), 'w')
-    f.write(output.encode(self.encoding, 'xmlcharrefreplace'))
-    f.close()
+    with open(format.dest(self.relpath), 'w') as f:
+      f.write(output.encode(self.encoding, 'xmlcharrefreplace'))
 
   def compact(self):
     self.tree = None