I am sending a plain text email as follows:

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText

def send_message():
    msg = MIMEMultipart('alternative')
    s = smtplib.SMTP('smtp.sendgrid.net', 587)
    s.login(USERNAME, PASSWORD)

    toEmail, fromEmail = [email protected], [email protected]
    msg['Subject'] = 'subject'
    msg['From'] = fromEmail
    body = 'This is the message'

    content = MIMEText(body, 'plain')
    msg.attach(content)
    s.sendmail(fromEmail, toEmail, msg.as_string())

In addition to this message, I would like to attach a txt file, ‘log_file.txt’. How would I attach a txt file here?

The same way, using msg.attach:

from email.mime.text import MIMEText

filename = "text.txt"
f = file(filename)
attachment = MIMEText(f.read())
attachment.add_header('Content-Disposition', 'attachment', filename=filename)           
msg.attach(attachment)

Since Python3.6, I would recommend start using EmailMessage instead of MimeMultipart. Fewer imports, fewer lines, no need to put the recipients both to the message headers and to the SMTP sender function parameter.

import smtplib
from email.message import EmailMessage

msg = EmailMessage()
msg["From"] = FROM_EMAIL
msg["Subject"] = "Subject"
msg["To"] = TO_EMAIL
msg.set_content("This is the message body")
msg.add_attachment(open(filename, "r").read(), filename="log_file.txt")

s = smtplib.SMTP('smtp.sendgrid.net', 587)
s.login(USERNAME, PASSWORD)
s.send_message(msg)

Even better is to install library envelope by pip3 install envelope that’s aim is to handle many things in a very intuitive manner:

from envelope import Envelope
from pathlib import Path

Envelope()\
    .from_(FROM_EMAIL)\
    .subject("Subject")\
    .to("to")\
    .message("message")\
    .attach(Path(filename))\
    .smtp("smtp.sendgrid.net", 587, USERNAME, PASSWORD)\
    .send()

It works for me

sender="[email protected]"
receivers="who"

msg = MIMEMultipart()
msg['Subject'] = 'subject'
msg['From'] = 'spider man'
msg['To'] = '[email protected]'
file="myfile.xls"

msg.attach(MIMEText("Labour"))
attachment = MIMEBase('application', 'octet-stream')
attachment.set_payload(open(file, 'rb').read())
encoders.encode_base64(attachment)
attachment.add_header('Content-Disposition', 'attachment; filename="%s"' % os.path.basename(file))
msg.attach(attachment)

print('Send email.')
conn.sendmail(sender, receivers, msg.as_string())
conn.close()