Resort to determining python version to work around base64 byte encoding issue.

Author: rossigee

prometheus_client/exposition.py

@@ -9,6 +9,7 @@
 from contextlib import closing
 from wsgiref.simple_server import make_server
 import base64
+import sys
 
 from . import core
 try:
@@ -145,8 +146,12 @@ def handle():
         '''Handler that implements HTTP Basic Auth.
         '''
         if username is not None and password is not None:
-            auth_value = bytes('{0}:{1}'.format(username, password), 'utf8')
-            auth_token = str(base64.b64encode(auth_value), 'utf8')
+            if sys.version_info >= (3,0):
+                auth_value = bytes('{0}:{1}'.format(username, password), 'utf8')
+                auth_token = str(base64.b64encode(auth_value), 'utf8')
+            else:
+                auth_value = '{0}:{1}'.format(username, password)
+                auth_token = base64.b64encode(auth_value)
             auth_header = "Basic {0}".format(auth_token)
             headers.append(['Authorization', auth_header])
         default_handler(url, method, timeout, headers, data)()