asynchronous_mail_send.md

Asynchronous Mail Send

Using asyncio (3.5+)

The built-in asyncio library can be used to send email in a non-blocking manner. asyncio helps us execute mail sending in a separate context, allowing us to continue the execution of business logic without waiting for all our emails to send first.

from sendgrid import SendGridAPIClient
from sendgrid.helpers.mail import Content, Mail, From, To, Mail
import os
import asyncio


sendgrid_client = SendGridAPIClient(
    api_key=os.environ.get('SENDGRID_API_KEY'))

from_email = From("test@example.com")
to_email = To("test1@example.com")

plain_text_content = Content("text/plain", "This is asynchronous sending test.")
html_content = Content("text/html", "<strong>This is asynchronous sending test.</strong>")

# instantiate `sendgrid.helpers.mail.Mail` objects
em1 = Mail(from_email, to_email, "Message #1", content)
em2 = Mail(from_email, to_email, "Message #2", content)
em3 = Mail(from_email, to_email, "Message #3", content)
em4 = Mail(from_email, to_email, "Message #4", content)
em5 = Mail(from_email, to_email, "Message #5", content)
em6 = Mail(from_email, to_email, "Message #6", content)
em7 = Mail(from_email, to_email, "Message #7", content)
em8 = Mail(from_email, to_email, "Message #8", content)
em9 = Mail(from_email, to_email, "Message #9", content)
em10 = Mail(from_email, to_email, "Message #10", content)


ems = [em1, em2, em3, em4, em5, em6, em7, em8, em9, em10]


async def send_email(n, email):
    '''
    send_mail wraps Twilio SendGrid's API client, and makes a POST request to
    the api/v3/mail/send endpoint with `email`.
    Args:
        email<sendgrid.helpers.mail.Mail>: single mail object.
    '''
    try:
        response = sendgrid_client.send(request_body=email)
        if response.status_code < 300:
            print("Email #{} processed".format(n), response.body, response.status_code)
    except urllib.error.HTTPError as e:
        e.read()


@asyncio.coroutine
def send_many(emails, cb):
    '''
    send_many creates a number of non-blocking tasks (to send email)
    that will run on the existing event loop. Due to non-blocking nature,
    you can include a callback that will run after all tasks have been queued.

    Args:
        emails<list>: contains any # of `sendgrid.helpers.mail.Mail`.
        cb<function>: a function that will execute immediately.
    '''
    print("START - sending emails ...")
    for n, em in enumerate(emails):
        asyncio.async(send_email(n, em))
    print("END - returning control...")
    cb()


def sample_cb():
    print("Executing callback now...")
    for i in range(0, 100):
        print(i)
    return


if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    task = asyncio.async(send_many(ems, sample_cb))
    loop.run_until_complete(task)