diff --git a/.travis.yml b/.travis.yml
index 7288a2a..1341a1d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,8 +1,6 @@
 language: python
 python:
-  - "2.6"
   - "2.7"
-  - "3.3"
   - "3.4"
   - "3.5"
   - "3.6"
diff --git a/gitdb/db/pack.py b/gitdb/db/pack.py
index 6b03d83..1e37d73 100644
--- a/gitdb/db/pack.py
+++ b/gitdb/db/pack.py
@@ -148,7 +148,7 @@ def update_cache(self, force=False):
         # packs are supposed to be prefixed with pack- by git-convention
         # get all pack files, figure out what changed
         pack_files = set(glob.glob(os.path.join(self.root_path(), "pack-*.pack")))
-        our_pack_files = set(item[1].pack().path() for item in self._entities)
+        our_pack_files = {item[1].pack().path() for item in self._entities}
 
         # new packs
         for pack_file in (pack_files - our_pack_files):
diff --git a/gitdb/db/ref.py b/gitdb/db/ref.py
index 94a2f01..2bb1de7 100644
--- a/gitdb/db/ref.py
+++ b/gitdb/db/ref.py
@@ -49,7 +49,7 @@ def _update_dbs_from_ref_file(self):
         # END handle alternates
 
         ref_paths_set = set(ref_paths)
-        cur_ref_paths_set = set(db.root_path() for db in self._dbs)
+        cur_ref_paths_set = {db.root_path() for db in self._dbs}
 
         # remove existing
         for path in (cur_ref_paths_set - ref_paths_set):
diff --git a/gitdb/test/lib.py b/gitdb/test/lib.py
index bbdd241..ab1842d 100644
--- a/gitdb/test/lib.py
+++ b/gitdb/test/lib.py
@@ -86,7 +86,7 @@ def wrapper(self):
             try:
                 return func(self, path)
             except Exception:
-                sys.stderr.write("Test %s.%s failed, output is at %r\n" % (type(self).__name__, func.__name__, path))
+                sys.stderr.write("Test {}.{} failed, output is at {!r}\n".format(type(self).__name__, func.__name__, path))
                 keep = True
                 raise
         finally:
diff --git a/gitdb/util.py b/gitdb/util.py
index 8a1819b..d680f97 100644
--- a/gitdb/util.py
+++ b/gitdb/util.py
@@ -19,10 +19,7 @@
 
 # initialize our global memory manager instance
 # Use it to free cached (and unused) resources.
-if sys.version_info < (2, 6):
-    mman = StaticWindowMapManager()
-else:
-    mman = SlidingWindowMapManager()
+mman = SlidingWindowMapManager()
 # END handle mman
 
 import hashlib
diff --git a/setup.py b/setup.py
index 4bff11d..27bb754 100755
--- a/setup.py
+++ b/setup.py
@@ -22,6 +22,7 @@
     zip_safe=False,
     install_requires=['smmap2 >= 2.0.0'],
     long_description="""GitDB is a pure-Python git object database""",
+    python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*',
     # See https://pypi.python.org/pypi?%3Aaction=list_classifiers
     classifiers=[
         "Development Status :: 5 - Production/Stable",
@@ -34,12 +35,10 @@
         "Operating System :: MacOS :: MacOS X",
         "Programming Language :: Python",
         "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.6",
         "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.2",
-        "Programming Language :: Python :: 3.3",
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
+        "Programming Language :: Python :: 3.6",
     ]
 )