Google API Client Libraryを使って、PythonからGmailを送信

send_gmail.py

from __future__ import with_statement
import pickle
import webbrowser
import httplib2
import base64
from sys import exit
from email.mime.text import MIMEText
from oauth2client import client
from apiclient.discovery import build

from apiclient import errors

def retrieve_authorize_code(flow):
    auth_url = flow.step1_get_authorize_url()
    webbrowser.open(auth_url)
    exit(0)

def retrieve_credential(flow):
    #auth_code = "auth_code"
    #credential = flow.step2_exchange(auth_code)

    #with open("credential.pickle", "w") as fpickle:
    #    pickle.dump(credential, fpickle)

    # load credential
    with open("credential.pickle", "r") as fpickle:
        credential = pickle.load(fpickle)

    return credential


def create_service(credential):
    http_auth = credential.authorize(httplib2.Http())
    return build("gmail", "v1", http=http_auth)

def create_mail(message_text, subject, to, from_):
    message = MIMEText(message_text)
    message["subject"] = subject
    message["to"] = to
    message["from"] = from_

    return {"raw": base64.urlsafe_b64encode(message.as_string())}

def send_mail(service, raw):
    try:
        message = service.users().messages().send(userId="me", body=raw).execute()
        print "A message sent. Id: {}".format(message["id"])

    except errors.HttpError, error:
        print "An error occurred: {}".format(error)

"""Main"""
flow = client.flow_from_clientsecrets(
    "client_secrets.json",
    scope = "https://www.googleapis.com/auth/gmail.send",
    redirect_uri = "urn:ietf:wg:oauth:2.0:oob")

# retrieve_authorize_code(flow)

credential = retrieve_credential(flow)

service = create_service(credential)

message_text = "hello, world!"
subject = "test subject"
to = "example@gmail.com"
from_ = "example@gmail.com"

mail = create_mail(message_text, subject, to, from_)

send_mail(service, mail)