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Parsing Traditional Messages

What happens when you receive an incoming message as a raw block of text and want to look inside? Well, the email module also provides support for parsing e-mail messages, re-constructing the same Message object that would have been used to create the message in the first place. (Of course, it does not matter whether the e-mail you are parsing was originally created in Python through the Message class, or whether some other e-mail program created it; the format is standard, so Python’s parsing should work either way.) After parsing the message, you can easily access individual headers and the body of the message using the same conventions as you used to create messages: headers look like the dictionary key-values of the Message, and the body can be fetched with a function.

A simple example of a parser is shown in trad_parse.py. All of the actual parsing takes place in the one-line function message_from_file(); everything else in the program listing is simply an illustration of how a Message object can be mined for headers and data.

import email

banner = '-' * 48
popular_headers = ('From', 'To', 'Subject', 'Date')
msg = email.message_from_file(open('message.txt'))
headers = sorted(msg.keys())

print banner
for header in headers:
    if header not in popular_headers:
        print header + ':', msg[header]
print banner
for header in headers:
    if header in popular_headers:
        print header + ':', msg[header]

print banner
if msg.is_multipart():
    print "This program cannot handle MIME multipart messages."
else:
    print msg.get_payload()

The output should be like this

[email protected]:~/Python_files# python trad_parse.py
------------------------------------------------
Message-ID: <[email protected]>
------------------------------------------------
Date:  Mon, 14 Jul 2014 14:33:54 +0200
From: Test Sender <[email protected]>
Subject: Test Message, Chapter 12
To: [email protected]
------------------------------------------------
Hello,
This is a test message.
-- Anonymous
[email protected]:~/Python_files#

As you can see, the Python Standard Library makes it quite easy both to create and then to parse standard Internet e-mail messages. Note that the email package also offers a message_from_string() function that, instead of taking a file, can simply be handed the string containing an e-mail message.