diff --git a/pelican/generators.py b/pelican/generators.py
index 2987dcfe..71208430 100644
--- a/pelican/generators.py
+++ b/pelican/generators.py
@@ -227,7 +227,7 @@ class ArticlesGenerator(Generator):
                 continue
 
             # if no category is set, use the name of the path as a category
-            if 'category' not in metadata.keys():
+            if 'category' not in metadata:
 
                 if os.path.dirname(f) == self.path:
                     category = self.settings['DEFAULT_CATEGORY']
@@ -238,8 +238,7 @@ class ArticlesGenerator(Generator):
                 if category != '':
                     metadata['category'] = Category(category, self.settings)
 
-            if 'date' not in metadata.keys()\
-                and self.settings['FALLBACK_ON_FS_DATE']:
+            if 'date' not in metadata and self.settings['FALLBACK_ON_FS_DATE']:
                     metadata['date'] = datetime.datetime.fromtimestamp(
                                         os.stat(f).st_ctime)
 
diff --git a/pelican/readers.py b/pelican/readers.py
index 632c72b9..d4e13b4d 100644
--- a/pelican/readers.py
+++ b/pelican/readers.py
@@ -145,7 +145,7 @@ def read_file(filename, fmt=None, settings=None):
     if not fmt:
         fmt = filename.split('.')[-1]
 
-    if fmt not in _EXTENSIONS.keys():
+    if fmt not in _EXTENSIONS:
         raise TypeError('Pelican does not know how to parse %s' % filename)
 
     reader = _EXTENSIONS[fmt](settings)
diff --git a/pelican/utils.py b/pelican/utils.py
index 1b84f108..7ffd9eb9 100644
--- a/pelican/utils.py
+++ b/pelican/utils.py
@@ -210,9 +210,6 @@ LAST_MTIME = 0
 def files_changed(path, extensions):
     """Return True if the files have changed since the last check"""
 
-    def with_extension(f):
-        return any(f.endswith(ext) for ext in extensions)
-
     def file_times(path):
         """Return the last time files have been modified"""
         for root, dirs, files in os.walk(path):
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 9654825e..40f710d9 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -3,11 +3,12 @@ try:
     import unittest2 as unittest
 except ImportError:
     import unittest  # NOQA
+
+import os
 import datetime
+import time
 
 from pelican import utils
-from pelican.contents import Article
-
 from support import get_article
 
 
@@ -73,3 +74,20 @@ class TestUtils(unittest.TestCase):
         self.assertIn(fr_article1, trans)
         self.assertNotIn(en_article1, trans)
         self.assertNotIn(fr_article1, index)
+
+    def test_files_changed(self):
+        "Test if file changes are correctly detected"
+
+        path = os.path.join(os.path.dirname(__file__), 'content')
+        filename = os.path.join(path, 'article_with_metadata.rst')
+        changed = utils.files_changed(path, 'rst')
+        self.assertEquals(changed, True)
+
+        changed = utils.files_changed(path, 'rst')
+        self.assertEquals(changed, False)
+
+        t = time.time()
+        os.utime(filename, (t, t))
+        changed = utils.files_changed(path, 'rst')
+        self.assertEquals(changed, True)
+        self.assertAlmostEqual(utils.LAST_MTIME, t, places=2)