Index: src/zc/buildout/__init__.py
===================================================================
--- src/zc/buildout/__init__.py	(revision 103702)
+++ src/zc/buildout/__init__.py	(working copy)
@@ -21,4 +21,4 @@
     """
 
     def __str__(self):
-        return " ".join(map(str, self))
+        return " ".join(map(str, self.args))
Index: src/zc/buildout/download.py
===================================================================
--- src/zc/buildout/download.py	(revision 103702)
+++ src/zc/buildout/download.py	(working copy)
@@ -24,15 +24,20 @@
 import re
 import shutil
 import tempfile
-import urllib
+import sys
+# Rename to _urllib on importing, as 2to3 will replace urlparse
+# below with urllib.parse
+if sys.version_info < (3,):
+    import urllib as _urllib
+else:
+    from urllib import request as _urllib
 import urlparse
 import zc.buildout
 
+class URLOpener(_urllib.FancyURLopener):
+    Http_error_default = _urllib.URLopener.http_error_default
 
-class URLOpener(urllib.FancyURLopener):
-    http_error_default = urllib.URLopener.http_error_default
 
-
 class ChecksumError(zc.buildout.UserError):
     pass
 
@@ -166,11 +171,11 @@
                 "Couldn't download %r in offline mode." % url)
 
         self.logger.info('Downloading %s' % url)
-        urllib._urlopener = url_opener
+        _urllib._urlopener = url_opener
         handle, tmp_path = tempfile.mkstemp(prefix='buildout-')
         try:
             try:
-                tmp_path, headers = urllib.urlretrieve(url, tmp_path)
+                tmp_path, headers = _urllib.urlretrieve(url, tmp_path)
                 if not check_md5sum(tmp_path, md5sum):
                     raise ChecksumError(
                         'MD5 checksum mismatch downloading %r' % url)
Index: src/zc/buildout/easy_install.py
===================================================================
--- src/zc/buildout/easy_install.py	(revision 103702)
+++ src/zc/buildout/easy_install.py	(working copy)
@@ -659,7 +659,7 @@
             try:
                 ws.resolve(requirements)
             except pkg_resources.DistributionNotFound, err:
-                [requirement] = err
+                requirement = err.args[0] # XXX - mvl - why was this list unpacking?
                 requirement = self._constrain(requirement)
                 if dest:
                     logger.debug('Getting required %r', str(requirement))
@@ -832,6 +832,13 @@
 
     return result[0]
 
+if sys.version_info <= (3,):
+    def _bytes(s):
+        return s
+else:
+    def _bytes(s):
+        return s.encode("ascii")
+
 def develop(setup, dest,
             build_ext=None,
             executable=sys.executable):
@@ -863,12 +870,12 @@
         undo.append(lambda: os.remove(tsetup))
         undo.append(lambda: os.close(fd))
 
-        os.write(fd, runsetup_template % dict(
+        os.write(fd, _bytes(runsetup_template % dict(
             setuptools=setuptools_loc,
             setupdir=directory,
             setup=setup,
             __file__ = setup,
-            ))
+            )))
 
         tmp3 = tempfile.mkdtemp('build', dir=dest)
         undo.append(lambda : shutil.rmtree(tmp3))
@@ -1144,7 +1151,7 @@
         sys.argv[:] = _args
         __file__ = _args[0]
         del _options, _args
-        execfile(__file__)
+        exec(compile(open(__file__).read(), __file__, 'exec'))
 
 if _interactive:
     del _interactive
@@ -1161,7 +1168,7 @@
 
 os.chdir(%(setupdir)r)
 sys.argv[0] = %(setup)r
-execfile(%(setup)r)
+exec(compile(open(%(setup)r).read(), %(setup)r, 'exec'))
 """
 
 class VersionConflict(zc.buildout.UserError):
Index: src/zc/buildout/buildout.py
===================================================================
--- src/zc/buildout/buildout.py	(revision 103702)
+++ src/zc/buildout/buildout.py	(working copy)
@@ -33,7 +33,19 @@
 import shutil
 import sys
 import tempfile
-import UserDict
+import base64
+if sys.version_info <= (3,):
+    from UserDict import DictMixin
+else:
+    from collections import MutableMapping
+    class DictMixin(MutableMapping):
+        def __len__(self):
+            # MutableMapping can't predefine __len__, since .keys() won't necessarily
+            # return a list. However, 2.x DictMixin assumes exactly that, and so can we here
+            return len(self.keys())
+        def __iter__(self):
+            # likewise
+            return iter(self.keys())
 import zc.buildout
 import zc.buildout.download
 import zc.buildout.easy_install
@@ -124,7 +136,7 @@
     }, 'DEFAULT_VALUE')
 
 
-class Buildout(UserDict.DictMixin):
+class Buildout(DictMixin):
 
     def __init__(self, config_file, cloptions,
                  user_defaults=True, windows_restart=False, command=None):
@@ -1014,7 +1026,7 @@
             group, entry, spec, v)
         raise
 
-class Options(UserDict.DictMixin):
+class Options(DictMixin):
 
     def __init__(self, buildout, section, data):
         self.buildout = buildout
@@ -1345,6 +1357,16 @@
     seen.pop()
     return result
 
+if sys.version_info <= (3,):
+    def _fsenc(s):
+        return s
+    def _tostring(b):
+        return b
+else:
+    def _fsenc(s):
+        return s.encode(sys.getfilesystemencoding())
+    def _tostring(b):
+        return b.decode("ascii")
 
 ignore_directories = '.svn', 'CVS'
 def _dir_hash(dir):
@@ -1355,11 +1377,11 @@
                         if (not (f.endswith('pyc') or f.endswith('pyo'))
                             and os.path.exists(os.path.join(dirpath, f)))
                         ]
-        hash.update(' '.join(dirnames))
-        hash.update(' '.join(filenames))
+        hash.update(_fsenc(' '.join(dirnames)))
+        hash.update(_fsenc(' '.join(filenames)))
         for name in filenames:
-            hash.update(open(os.path.join(dirpath, name)).read())
-    return hash.digest().encode('base64').strip()
+            hash.update(open(os.path.join(dirpath, name), 'rb').read())
+    return _tostring(base64.encodestring(hash.digest()).strip())
 
 def _dists_sig(dists):
     result = []
Index: setup.py
===================================================================
--- setup.py	(revision 103702)
+++ setup.py	(working copy)
@@ -17,6 +17,9 @@
 import os
 from setuptools import setup
 
+import setuptools
+setuptools.run_2to3=True
+
 def read(*rnames):
     return open(os.path.join(os.path.dirname(__file__), *rnames)).read()