diff --git a/recipes/recipe_modules/bot_update/resources/bot_update.py b/recipes/recipe_modules/bot_update/resources/bot_update.py
index 94e27f741..7d73447fe 100755
--- a/recipes/recipe_modules/bot_update/resources/bot_update.py
+++ b/recipes/recipe_modules/bot_update/resources/bot_update.py
@@ -5,9 +5,9 @@
 
 # TODO(hinoka): Use logging.
 
+from __future__ import division
 from __future__ import print_function
 
-import cStringIO
 import codecs
 from contextlib import contextmanager
 import copy
@@ -18,19 +18,23 @@ import json
 import optparse
 import os
 import pprint
-import random
 import re
 import subprocess
 import sys
 import tempfile
 import threading
 import time
-import urllib2
-import urlparse
 import uuid
 
 import os.path as path
 
+# TODO(crbug.com/1227140): Clean up when py2 is no longer supported.
+from io import BytesIO
+try:
+  import urlparse
+except ImportError:  # pragma: no cover
+  import urllib.parse as urlparse
+
 # How many bytes at a time to read from pipes.
 BUF_SIZE = 256
 
@@ -94,7 +98,7 @@ GCLIENT_PATH = path.join(DEPOT_TOOLS_DIR, 'gclient.py')
 
 class SubprocessFailed(Exception):
   def __init__(self, message, code, output):
-    Exception.__init__(self, message)
+    self.message = message
     self.code = code
     self.output = output
 
@@ -161,6 +165,14 @@ def _terminate_process(proc):
   proc.terminate()
 
 
+# TODO(crbug.com/1227140): Clean up when py2 is no longer supported.
+def _stdout_write(buf):
+  try:
+    sys.stdout.buffer.write(buf)
+  except AttributeError:
+    sys.stdout.write(buf)
+
+
 def call(*args, **kwargs):  # pragma: no cover
   """Interactive subprocess call."""
   kwargs['stdout'] = subprocess.PIPE
@@ -170,7 +182,7 @@ def call(*args, **kwargs):  # pragma: no cover
   stdin_data = kwargs.pop('stdin_data', None)
   if stdin_data:
     kwargs['stdin'] = subprocess.PIPE
-  out = cStringIO.StringIO()
+  out = BytesIO()
   new_env = kwargs.get('env', {})
   env = os.environ.copy()
   env.update(new_env)
@@ -209,17 +221,17 @@ def call(*args, **kwargs):  # pragma: no cover
     if hanging_cr:
       buf = buf[:-1]
     buf = buf.replace('\r\n', '\n').replace('\r', '\n')
-    sys.stdout.write(buf)
+    _stdout_write(buf)
     out.write(buf)
   if hanging_cr:
-    sys.stdout.write('\n')
+    _stdout_write('\n')
     out.write('\n')
   for observer in observers:
     observer.shutdown()
 
   code = proc.wait()
   elapsed_time = ((time.time() - start_time) / 60.0)
-  outval = out.getvalue()
+  outval = out.getvalue().decode('utf-8')
   if code:
     print('%s ===Failed in %.1f mins of %s ===' %
           (datetime.now(), elapsed_time, ' '.join(args)))
@@ -455,7 +467,7 @@ def create_manifest():
         for path, info in json.load(f).items()
         if info['rev'] is not None
       }
-  except ValueError, SubprocessFailed:
+  except (ValueError, SubprocessFailed):
     return {}
   finally:
     os.remove(fname)
@@ -598,7 +610,7 @@ def _maybe_break_locks(checkout_path, tries=3):
             print('FAILED to break lock: %s: %s' % (to_break, ex))
             raise
 
-  for _ in xrange(tries):
+  for _ in range(tries):
     try:
       attempt()
       return
@@ -816,7 +828,7 @@ def emit_json(out_file, did_run, **kwargs):
   output.update({'did_run': did_run})
   output.update(kwargs)
   with open(out_file, 'wb') as f:
-    f.write(json.dumps(output, sort_keys=True))
+    f.write(json.dumps(output, sort_keys=True).encode('utf-8'))
 
 
 @_set_git_config