Make 2/3 compatible code with python-modernize
diff --git a/googleapiclient/model.py b/googleapiclient/model.py
index e55b4fa..9be5a59 100644
--- a/googleapiclient/model.py
+++ b/googleapiclient/model.py
@@ -20,6 +20,7 @@
 object representation.
 """
 from __future__ import absolute_import
+import six
 
 __author__ = 'jcgregorio@google.com (Joe Gregorio)'
 
@@ -105,11 +106,11 @@
     if dump_request_response:
       logging.info('--request-start--')
       logging.info('-headers-start-')
-      for h, v in headers.iteritems():
+      for h, v in six.iteritems(headers):
         logging.info('%s: %s', h, v)
       logging.info('-headers-end-')
       logging.info('-path-parameters-start-')
-      for h, v in path_params.iteritems():
+      for h, v in six.iteritems(path_params):
         logging.info('%s: %s', h, v)
       logging.info('-path-parameters-end-')
       logging.info('body: %s', body)
@@ -160,13 +161,13 @@
     if self.alt_param is not None:
       params.update({'alt': self.alt_param})
     astuples = []
-    for key, value in params.iteritems():
+    for key, value in six.iteritems(params):
       if type(value) == type([]):
         for x in value:
           x = x.encode('utf-8')
           astuples.append((key, x))
       else:
-        if isinstance(value, unicode) and callable(value.encode):
+        if isinstance(value, six.text_type) and callable(value.encode):
           value = value.encode('utf-8')
         astuples.append((key, value))
     return '?' + urllib.urlencode(astuples)
@@ -175,7 +176,7 @@
     """Logs debugging information about the response if requested."""
     if dump_request_response:
       logging.info('--response-start--')
-      for h, v in resp.iteritems():
+      for h, v in six.iteritems(resp):
         logging.info('%s: %s', h, v)
       if content:
         logging.info(content)
@@ -360,7 +361,7 @@
       body=makepatch(original, item)).execute()
   """
   patch = {}
-  for key, original_value in original.iteritems():
+  for key, original_value in six.iteritems(original):
     modified_value = modified.get(key, None)
     if modified_value is None:
       # Use None to signal that the element is deleted