Update example so it works under Python 3.

demo/example.py

@@ -1,6 +1,11 @@
 import sys
+
 from yubico_client import Yubico
 from yubico_client import yubico_exceptions
+from yubico_client.py3 import PY3
+
+if PY3:
+    raw_input = input
 
 client_id = raw_input('Enter your client id: ')
 secret_key = raw_input('Enter your secret key (optional): ')
@@ -19,17 +24,20 @@
 
 try:
     status = client.verify(token)
-except yubico_exceptions.InvalidClientIdError, e:
-    print 'Client with id %s does not exist' % (e.client_id)
+except yubico_exceptions.InvalidClientIdError:
+    e = sys.exc_info()[1]
+    print('Client with id %s does not exist' % (e.client_id))
     sys.exit(1)
 except yubico_exceptions.SignatureVerificationError:
-    print 'Signature verification failed'
+    print('Signature verification failed')
     sys.exit(1)
-except yubico_exceptions.StatusCodeError, e:
-    print 'Negative status code was returned: %s' % (e.status_code)
+except yubico_exceptions.StatusCodeError:
+    e = sys.exc_info()[1]
+    print('Negative status code was returned: %s' % (e.status_code))
     sys.exit(1)
 
 if status:
-    print 'Success, the provided OTP is valid'
+    print('Success, the provided OTP is valid')
 else:
-    print 'No response from the servers or received other negative status code'
+    print('No response from the servers or received other negative '
+          'status code')