diff --git a/python/ycm/base.py b/python/ycm/base.py
index e64667d4..b4659bd8 100644
--- a/python/ycm/base.py
+++ b/python/ycm/base.py
@@ -15,6 +15,15 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
+from future.utils import iteritems
 from ycm import vimsupport
 from ycmd import user_options_store
 from ycmd import request_wrap
@@ -29,7 +38,7 @@ def BuildServerConf():
 
   vim_globals = vimsupport.GetReadOnlyVimGlobals( force_python_objects = True )
   server_conf = {}
-  for key, value in vim_globals.items():
+  for key, value in iteritems( vim_globals ):
     if not key.startswith( YCM_VAR_PREFIX ):
       continue
     try:
@@ -45,7 +54,7 @@ def BuildServerConf():
 def LoadJsonDefaultsIntoVim():
   defaults = user_options_store.DefaultOptions()
   vim_defaults = {}
-  for key, value in defaults.iteritems():
+  for key, value in iteritems( defaults ):
     vim_defaults[ 'ycm_' + key ] = value
 
   vimsupport.LoadDictIntoVimGlobals( vim_defaults, overwrite = False )
@@ -115,7 +124,7 @@ def AdjustCandidateInsertionText( candidates ):
 
   new_candidates = []
   for candidate in candidates:
-    if type( candidate ) is dict:
+    if isinstance( candidate, dict ):
       new_candidate = candidate.copy()
 
       if not 'abbr' in new_candidate:
@@ -127,7 +136,7 @@ def AdjustCandidateInsertionText( candidates ):
 
       new_candidates.append( new_candidate )
 
-    elif type( candidate ) is str:
+    elif isinstance( candidate, str ) or isinstance( candidate, bytes ):
       new_candidates.append(
         { 'abbr': candidate,
           'word': NewCandidateInsertionText( candidate, text_after_cursor ) } )
diff --git a/python/ycm/client/base_request.py b/python/ycm/client/base_request.py
index 83b4159b..c3eb2224 100644
--- a/python/ycm/client/base_request.py
+++ b/python/ycm/client/base_request.py
@@ -15,8 +15,16 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 import requests
-import urlparse
+import urllib.parse
 import json
 from base64 import b64decode, b64encode
 from retries import retries
@@ -133,7 +141,7 @@ class BaseRequest( object ):
     headers = dict( _HEADERS )
     headers[ _HMAC_HEADER ] = b64encode(
         CreateRequestHmac( method,
-                           urlparse.urlparse( request_uri ).path,
+                           urllib.parse.urlparse( request_uri ).path,
                            request_body,
                            BaseRequest.hmac_secret ) )
     return headers
@@ -196,7 +204,7 @@ def _ValidateResponseObject( response ):
 
 
 def _BuildUri( handler ):
-  return urlparse.urljoin( BaseRequest.server_location, handler )
+  return urllib.parse.urljoin( BaseRequest.server_location, handler )
 
 
 SERVER_HEALTHY = False
diff --git a/python/ycm/client/command_request.py b/python/ycm/client/command_request.py
index 8b7c12cb..28dc1278 100644
--- a/python/ycm/client/command_request.py
+++ b/python/ycm/client/command_request.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 import vim
 from ycm.client.base_request import BaseRequest, BuildRequestData, ServerError
 from ycm import vimsupport
diff --git a/python/ycm/client/completer_available_request.py b/python/ycm/client/completer_available_request.py
index 620edfa0..a90ef1cb 100644
--- a/python/ycm/client/completer_available_request.py
+++ b/python/ycm/client/completer_available_request.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.client.base_request import ( BaseRequest, BuildRequestData,
                                       HandleServerException )
 
diff --git a/python/ycm/client/completion_request.py b/python/ycm/client/completion_request.py
index e162b8e5..5b66ef3e 100644
--- a/python/ycm/client/completion_request.py
+++ b/python/ycm/client/completion_request.py
@@ -15,7 +15,15 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
-from ycmd.utils import ToBytes, ToUnicode
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
+from ycmd.utils import ToUnicode
 from ycm.client.base_request import ( BaseRequest, JsonFromFuture,
                                       HandleServerException,
                                       MakeServerException )
@@ -69,22 +77,22 @@ def ConvertCompletionDataToVimData( completion_data ):
 
   if ( 'extra_data' in completion_data and
        'doc_string' in completion_data[ 'extra_data' ] ):
-    doc_string = ToBytes( completion_data[ 'extra_data' ][ 'doc_string' ] )
+    doc_string = completion_data[ 'extra_data' ][ 'doc_string' ]
   else:
     doc_string = ""
 
   if 'insertion_text' in completion_data:
-    vim_data[ 'word' ] = ToBytes( completion_data[ 'insertion_text' ] )
+    vim_data[ 'word' ] = completion_data[ 'insertion_text' ]
   if 'menu_text' in completion_data:
-    vim_data[ 'abbr' ] = ToBytes( completion_data[ 'menu_text' ] )
+    vim_data[ 'abbr' ] = completion_data[ 'menu_text' ]
   if 'extra_menu_info' in completion_data:
-    vim_data[ 'menu' ] = ToBytes( completion_data[ 'extra_menu_info' ] )
+    vim_data[ 'menu' ] = completion_data[ 'extra_menu_info' ]
   if 'kind' in completion_data:
     kind = ToUnicode( completion_data[ 'kind' ] )
     if kind:
-      vim_data[ 'kind' ] = ToBytes( kind[ 0 ].lower() )
+      vim_data[ 'kind' ] = kind[ 0 ].lower()
   if 'detailed_info' in completion_data:
-    vim_data[ 'info' ] = ToBytes( completion_data[ 'detailed_info' ] )
+    vim_data[ 'info' ] = completion_data[ 'detailed_info' ]
     if doc_string:
       vim_data[ 'info' ] += '\n' + doc_string
   elif doc_string:
diff --git a/python/ycm/client/event_notification.py b/python/ycm/client/event_notification.py
index 2200fc63..77e05a87 100644
--- a/python/ycm/client/event_notification.py
+++ b/python/ycm/client/event_notification.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm import vimsupport
 from ycmd.responses import UnknownExtraConf
 from ycm.client.base_request import ( BaseRequest, BuildRequestData,
diff --git a/python/ycm/client/omni_completion_request.py b/python/ycm/client/omni_completion_request.py
index 48cb112f..2bcb2911 100644
--- a/python/ycm/client/omni_completion_request.py
+++ b/python/ycm/client/omni_completion_request.py
@@ -15,7 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
-from ycmd.utils import ToBytes
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.client.completion_request import CompletionRequest
 
 
@@ -46,15 +53,15 @@ def ConvertVimDataToCompletionData( vim_data ):
   completion_data = {}
 
   if 'word' in vim_data:
-    completion_data[ 'insertion_text' ] = ToBytes( vim_data[ 'word' ] )
+    completion_data[ 'insertion_text' ] = vim_data[ 'word' ]
   if 'abbr' in vim_data:
-    completion_data[ 'menu_text' ] = ToBytes( vim_data[ 'abbr' ] )
+    completion_data[ 'menu_text' ] = vim_data[ 'abbr' ]
   if 'menu' in vim_data:
-    completion_data[ 'extra_menu_info' ] = ToBytes( vim_data[ 'menu' ] )
+    completion_data[ 'extra_menu_info' ] = vim_data[ 'menu' ]
   if 'kind' in vim_data:
-    completion_data[ 'kind' ] = [ ToBytes( vim_data[ 'kind' ] ) ]
+    completion_data[ 'kind' ] = [ vim_data[ 'kind' ] ]
   if 'info' in vim_data:
-    completion_data[ 'detailed_info' ] = ToBytes( vim_data[ 'info' ] )
+    completion_data[ 'detailed_info' ] = vim_data[ 'info' ]
 
   return completion_data
 
diff --git a/python/ycm/client/tests/command_request_test.py b/python/ycm/client/tests/command_request_test.py
index d62518ba..40cdaa57 100644
--- a/python/ycm/client/tests/command_request_test.py
+++ b/python/ycm/client/tests/command_request_test.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.test_utils import MockVimModule
 MockVimModule()
 
@@ -24,7 +32,7 @@ from nose.tools import ok_
 from ycm.client.command_request import CommandRequest
 
 
-class GoToResponse_QuickFix_test:
+class GoToResponse_QuickFix_test( object ):
   """This class tests the generation of QuickFix lists for GoTo responses which
   return multiple locations, such as the Python completer and JavaScript
   completer. It mostly proves that we use 1-based indexing for the column
@@ -92,7 +100,7 @@ class GoToResponse_QuickFix_test:
     ] )
 
 
-class Response_Detection_test:
+class Response_Detection_test( object ):
 
   def BasicResponse_test( self ):
     def _BasicResponseTest( command, response ):
diff --git a/python/ycm/client/tests/completion_request_test.py b/python/ycm/client/tests/completion_request_test.py
index c1b19534..d2417b8e 100644
--- a/python/ycm/client/tests/completion_request_test.py
+++ b/python/ycm/client/tests/completion_request_test.py
@@ -15,13 +15,21 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from nose.tools import eq_
 from ycm.test_utils import MockVimModule
 vim_mock = MockVimModule()
 
 from .. import completion_request
 
-class ConvertCompletionResponseToVimDatas_test:
+class ConvertCompletionResponseToVimDatas_test( object ):
   """ This class tests the
       completion_request._ConvertCompletionResponseToVimDatas method """
 
@@ -32,10 +40,10 @@ class ConvertCompletionResponseToVimDatas_test:
     try:
       eq_( expected_vim_data, vim_data )
     except:
-      print "Expected:\n'{0}'\nwhen parsing:\n'{1}'\nBut found:\n'{2}'".format(
+      print( "Expected:\n'{0}'\nwhen parsing:\n'{1}'\nBut found:\n'{2}'".format(
           expected_vim_data,
           completion_data,
-          vim_data )
+          vim_data ) )
       raise
 
 
diff --git a/python/ycm/client/ycmd_keepalive.py b/python/ycm/client/ycmd_keepalive.py
index b9980b53..fca59f42 100644
--- a/python/ycm/client/ycmd_keepalive.py
+++ b/python/ycm/client/ycmd_keepalive.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 import time
 from threading import Thread
 from ycm.client.base_request import BaseRequest
diff --git a/python/ycm/diagnostic_interface.py b/python/ycm/diagnostic_interface.py
index 03b8de02..6cea2e73 100644
--- a/python/ycm/diagnostic_interface.py
+++ b/python/ycm/diagnostic_interface.py
@@ -15,6 +15,15 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
+from future.utils import itervalues, iteritems
 from collections import defaultdict, namedtuple
 from ycm import vimsupport
 import vim
@@ -95,8 +104,8 @@ class DiagnosticInterface( object ):
     line_to_diags = self._buffer_number_to_line_to_diags[
       vim.current.buffer.number ]
 
-    for diags in line_to_diags.itervalues():
-      matched_diags.extend( filter( predicate, diags ) )
+    for diags in itervalues( line_to_diags ):
+      matched_diags.extend( list( filter( predicate, diags ) ) )
     return matched_diags
 
 
@@ -104,7 +113,7 @@ def _UpdateSquiggles( buffer_number_to_line_to_diags ):
   vimsupport.ClearYcmSyntaxMatches()
   line_to_diags = buffer_number_to_line_to_diags[ vim.current.buffer.number ]
 
-  for diags in line_to_diags.itervalues():
+  for diags in itervalues( line_to_diags ):
     for diag in diags:
       location_extent = diag[ 'location_extent' ]
       is_error = _DiagnosticIsError( diag )
@@ -168,11 +177,11 @@ def _GetKeptAndNewSigns( placed_signs, buffer_number_to_line_to_diags,
                          next_sign_id ):
   new_signs = []
   kept_signs = []
-  for buffer_number, line_to_diags in buffer_number_to_line_to_diags.iteritems():
+  for buffer_number, line_to_diags in iteritems( buffer_number_to_line_to_diags ):
     if not vimsupport.BufferIsVisible( buffer_number ):
       continue
 
-    for line, diags in line_to_diags.iteritems():
+    for line, diags in iteritems( line_to_diags ):
       for diag in diags:
         sign = _DiagSignPlacement( next_sign_id,
                                    line,
@@ -217,8 +226,8 @@ def _ConvertDiagListToDict( diag_list ):
     line_number = location[ 'line_num' ]
     buffer_to_line_to_diags[ buffer_number ][ line_number ].append( diag )
 
-  for line_to_diags in buffer_to_line_to_diags.itervalues():
-    for diags in line_to_diags.itervalues():
+  for line_to_diags in itervalues( buffer_to_line_to_diags ):
+    for diags in itervalues( line_to_diags ):
       # We also want errors to be listed before warnings so that errors aren't
       # hidden by the warnings; Vim won't place a sign oven an existing one.
       diags.sort( key = lambda diag: ( diag[ 'location' ][ 'column_num' ],
diff --git a/python/ycm/omni_completer.py b/python/ycm/omni_completer.py
index e5a3c76c..e9703311 100644
--- a/python/ycm/omni_completer.py
+++ b/python/ycm/omni_completer.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 import vim
 from ycm import vimsupport
 from ycmd.completers.completer import Completer
@@ -84,7 +92,7 @@ class OmniCompleter( Completer ):
       if not hasattr( items, '__iter__' ):
         raise TypeError( OMNIFUNC_NOT_LIST )
 
-      return filter( bool, items )
+      return list( filter( bool, items ) )
     except ( TypeError, ValueError, vim.error ) as error:
       vimsupport.PostVimMessage(
         OMNIFUNC_RETURNED_BAD_VALUE + ' ' + str( error ) )
diff --git a/python/ycm/paths.py b/python/ycm/paths.py
index 9ba85320..e23522a3 100644
--- a/python/ycm/paths.py
+++ b/python/ycm/paths.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 import os
 import sys
 import vim
diff --git a/python/ycm/syntax_parse.py b/python/ycm/syntax_parse.py
index f61b445c..e3299e46 100644
--- a/python/ycm/syntax_parse.py
+++ b/python/ycm/syntax_parse.py
@@ -15,6 +15,15 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
+from future.utils import itervalues
 import re
 import vim
 from ycm import vimsupport
@@ -174,7 +183,7 @@ def _ConnectGroupChildren( group_name_to_group ):
         parent_names.append( line[ len( links_to ): ] )
     return parent_names
 
-  for group in group_name_to_group.itervalues():
+  for group in itervalues( group_name_to_group ):
     parent_names = GetParentNames( group )
 
     for parent_name in parent_names:
diff --git a/python/ycm/test_utils.py b/python/ycm/test_utils.py
index 0c60f49c..1bb5cd9c 100644
--- a/python/ycm/test_utils.py
+++ b/python/ycm/test_utils.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from mock import MagicMock
 from hamcrest import assert_that, equal_to
 import re
diff --git a/python/ycm/tests/base_test.py b/python/ycm/tests/base_test.py
index 11e4ae79..26153ccf 100644
--- a/python/ycm/tests/base_test.py
+++ b/python/ycm/tests/base_test.py
@@ -17,6 +17,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 import contextlib
 from nose.tools import eq_, ok_
 from mock import patch
diff --git a/python/ycm/tests/event_notification_test.py b/python/ycm/tests/event_notification_test.py
index 4bfb7895..328c629e 100644
--- a/python/ycm/tests/event_notification_test.py
+++ b/python/ycm/tests/event_notification_test.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.test_utils import MockVimModule, ExtendedMock
 MockVimModule()
 
diff --git a/python/ycm/tests/omni_completion_request_tests.py b/python/ycm/tests/omni_completion_request_tests.py
index f605db3e..4f7a6822 100644
--- a/python/ycm/tests/omni_completion_request_tests.py
+++ b/python/ycm/tests/omni_completion_request_tests.py
@@ -15,6 +15,13 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
 
 from mock import MagicMock
 from nose.tools import eq_
diff --git a/python/ycm/tests/paths_test.py b/python/ycm/tests/paths_test.py
index eb1d1ba0..06071a34 100644
--- a/python/ycm/tests/paths_test.py
+++ b/python/ycm/tests/paths_test.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.test_utils import MockVimModule
 MockVimModule()
 
diff --git a/python/ycm/tests/postcomplete_tests.py b/python/ycm/tests/postcomplete_tests.py
index aaf8bc26..6a4b6a9f 100644
--- a/python/ycm/tests/postcomplete_tests.py
+++ b/python/ycm/tests/postcomplete_tests.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.test_utils import MockVimModule
 MockVimModule()
 
diff --git a/python/ycm/tests/syntax_parse_test.py b/python/ycm/tests/syntax_parse_test.py
index 276c6796..d1270677 100644
--- a/python/ycm/tests/syntax_parse_test.py
+++ b/python/ycm/tests/syntax_parse_test.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.test_utils import MockVimModule
 MockVimModule()
 
diff --git a/python/ycm/tests/vimsupport_test.py b/python/ycm/tests/vimsupport_test.py
index 7f8de3c5..2cea87cd 100644
--- a/python/ycm/tests/vimsupport_test.py
+++ b/python/ycm/tests/vimsupport_test.py
@@ -15,6 +15,14 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
 from ycm.test_utils import ExtendedMock, MockVimModule, MockVimCommand
 MockVimModule()
 
@@ -565,7 +573,7 @@ def ReplaceChunksInBuffer_UnsortedChunks_test():
   eq_( expected_buffer, result_buffer )
 
 
-class MockBuffer( ):
+class MockBuffer( object ):
   """An object that looks like a vim.buffer object, enough for ReplaceChunk to
   generate a location list"""
 
@@ -1167,27 +1175,13 @@ def BufferIsVisibleForFilename_test():
     eq_( vimsupport.BufferIsVisibleForFilename( 'another_filename' ), False )
 
 
+@patch( 'ycm.vimsupport.GetBufferNumberForFilename',
+        side_effect = [ 2, 5, -1 ] )
 @patch( 'vim.command',
         side_effect = MockVimCommand,
-        new_callable=ExtendedMock )
-def CloseBuffersForFilename_test( vim_command ):
-  buffers = [
-    {
-      'number': 2,
-      'filename': os.path.realpath( 'some_filename' ),
-    },
-    {
-      'number': 5,
-      'filename': os.path.realpath( 'some_filename' ),
-    },
-    {
-      'number': 1,
-      'filename': os.path.realpath( 'another_filename' )
-    }
-  ]
-
-  with patch( 'vim.buffers', buffers ):
-    vimsupport.CloseBuffersForFilename( 'some_filename' )
+        new_callable = ExtendedMock )
+def CloseBuffersForFilename_test( vim_command, *args ):
+  vimsupport.CloseBuffersForFilename( 'some_filename' )
 
   vim_command.assert_has_exact_calls( [
     call( 'silent! bwipeout! 2' ),
@@ -1195,8 +1189,8 @@ def CloseBuffersForFilename_test( vim_command ):
   ], any_order = True )
 
 
-@patch( 'vim.command', new_callable=ExtendedMock )
-@patch( 'vim.current', new_callable=ExtendedMock )
+@patch( 'vim.command', new_callable = ExtendedMock )
+@patch( 'vim.current', new_callable = ExtendedMock )
 def OpenFilename_test( vim_current, vim_command ):
   # Options used to open a logfile
   options = {
diff --git a/python/ycm/vimsupport.py b/python/ycm/vimsupport.py
index 0ed090f9..2a3ad5fa 100644
--- a/python/ycm/vimsupport.py
+++ b/python/ycm/vimsupport.py
@@ -15,13 +15,22 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
+from future.utils import iterkeys
 import vim
 import os
 import tempfile
 import json
 import re
 from collections import defaultdict
-from ycmd.utils import ToBytes, ToUnicode
+from ycmd.utils import ToUnicode
 from ycmd import user_options_store
 
 BUFFER_COMMAND_MAP = { 'same-buffer'      : 'edit',
@@ -277,7 +286,7 @@ def ConvertDiagnosticsToQfList( diagnostics ):
       'bufnr' : GetBufferNumberForFilename( location[ 'filepath' ] ),
       'lnum'  : line_num,
       'col'   : location[ 'column_num' ],
-      'text'  : ToBytes( text ),
+      'text'  : text,
       'type'  : diagnostic[ 'kind' ][ 0 ],
       'valid' : 1
     }
@@ -310,7 +319,7 @@ def GetReadOnlyVimGlobals( force_python_objects = False ):
 
 def VimExpressionToPythonType( vim_expression ):
   result = vim.eval( vim_expression )
-  if not isinstance( result, basestring ):
+  if not isinstance( result, str ):
     return result
   try:
     return int( result )
@@ -607,7 +616,7 @@ def ReplaceChunks( chunks ):
   chunks_by_file = _SortChunksByFile( chunks )
 
   # We sort the file list simply to enable repeatable testing
-  sorted_file_list = sorted( chunks_by_file.iterkeys() )
+  sorted_file_list = sorted( iterkeys( chunks_by_file ) )
 
   # Make sure the user is prepared to have her screen mutilated by the new
   # buffers
@@ -885,7 +894,7 @@ def OpenFilename( filename, options = {} ):
 
   # There is no command in Vim to return to the previous tab so we need to
   # remember the current tab if needed.
-  if not focus and command is 'tabedit':
+  if not focus and command == 'tabedit':
     previous_tab = GetIntValue( 'tabpagenr()' )
   else:
     previous_tab = None
@@ -920,7 +929,7 @@ def OpenFilename( filename, options = {} ):
   # focus back (if the focus option is disabled) when opening a new tab or
   # window.
   if not focus:
-    if command is 'tabedit':
+    if command == 'tabedit':
       JumpToTab( previous_tab )
     if command in [ 'split', 'vsplit' ]:
       JumpToPreviousWindow()
@@ -930,9 +939,9 @@ def _SetUpLoadedBuffer( command, filename, fix, position, watch ):
   """After opening a buffer, configure it according to the supplied options,
   which are as defined by the OpenFilename method."""
 
-  if command is 'split':
+  if command == 'split':
     vim.current.window.options[ 'winfixheight' ] = fix
-  if command is 'vsplit':
+  if command == 'vsplit':
     vim.current.window.options[ 'winfixwidth' ] = fix
 
   if watch:
@@ -940,6 +949,6 @@ def _SetUpLoadedBuffer( command, filename, fix, position, watch ):
     vim.command( "exec 'au BufEnter <buffer> :silent! checktime {0}'"
                  .format( filename ) )
 
-  if position is 'end':
+  if position == 'end':
     vim.command( 'silent! normal G zz' )
 
diff --git a/python/ycm/youcompleteme.py b/python/ycm/youcompleteme.py
index cf3f4f17..dab6ed67 100644
--- a/python/ycm/youcompleteme.py
+++ b/python/ycm/youcompleteme.py
@@ -15,6 +15,15 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import unicode_literals
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+from future import standard_library
+standard_library.install_aliases()
+from builtins import *  # noqa
+
+from future.utils import iteritems
 import os
 import vim
 import tempfile
@@ -303,7 +312,7 @@ class YouCompleteMe( object ):
 
   def GetCompleteDoneHooks( self ):
     filetypes = vimsupport.CurrentFiletypes()
-    for key, value in self._complete_done_hooks.iteritems():
+    for key, value in iteritems( self._complete_done_hooks ):
       if key in filetypes:
         yield value