python3 send email via gmail API

sendmail.py

from apiclient.discovery import build
from apiclient import errors
from httplib2 import Http
from oauth2client import file, client, tools
from email.mime.text import MIMEText
from base64 import urlsafe_b64encode


SENDER = <sender>
RECIPIENT = <recipient>
SUBJECT = <subject>
CONTENT = <content>
SCOPE = 'https://www.googleapis.com/auth/gmail.compose' # Allows sending only, not reading

# Initialize the object for the Gmail API
# https://developers.google.com/gmail/api/quickstart/python
store = file.Storage('credentials.json')
creds = store.get()
if not creds or creds.invalid:
    flow = client.flow_from_clientsecrets('client_secret.json', SCOPE)
    creds = tools.run_flow(flow, store)
service = build('gmail', 'v1', http=creds.authorize(Http()))


# https://developers.google.com/gmail/api/guides/sending
def create_message(sender, to, subject, message_text):
  """Create a message for an email.

  Args:
    sender: Email address of the sender.
    to: Email address of the receiver.
    subject: The subject of the email message.
    message_text: The text of the email message.

  Returns:
    An object containing a base64url encoded email object.
  """
  message = MIMEText(message_text)
  message['to'] = to
  message['from'] = sender
  message['subject'] = subject
  encoded_message = urlsafe_b64encode(message.as_bytes())
  return {'raw': encoded_message.decode()}


# https://developers.google.com/gmail/api/guides/sending
def send_message(service, user_id, message):
  """Send an email message.

  Args:
    service: Authorized Gmail API service instance.
    user_id: User's email address. The special value "me"
    can be used to indicate the authenticated user.
    message: Message to be sent.

  Returns:
    Sent Message.
  """
  try:
    message = (service.users().messages().send(userId=user_id, body=message)
               .execute())
    print('Message Id: %s' % message['id'])
    return message
  #except errors.HttpError, error:
  except:
    print('An error occurred: %s' % error)


raw_msg = create_message(SENDER, RECIPIENT, SUBJECT, CONTENT)
send_message(service, "me", raw_msg)

I used
from googleapiclient.errors import HttpError
except HttpError as error: