TweetFollow Us on Twitter

Mac in the Shell: Python Text Parsing

Volume Number: 25
Issue Number: 07
Column Tag: Mac in the Shell

Mac in the Shell: Python Text Parsing

Automating entries through keyword searching

by Edward Marczak

Introduction

We've been covering Python basics over the last several columns. This month, we'll hit something with a little practicality: text processing. While computers are really good with numbers, people are really good with words. More often than not, input from people comes as text. Turns out that Python is pretty good at dealing with text processing and manipulation. Let's have a closer look, shall we?

More To The Story

OK, there's a little bit more to the story. I've dealt with e-mail systems and e-mail processing for a very long time. (Let's just say that I started with sendmail before it used m4, mmmmkay?). Oftentimes, though, we want a program dealing with incoming mail. This may be for the purposes of a mailing list, for auto-response or to parse the e-mail and then put relevant bits into a database.

E-mail is either really complex or really simple, depending on how you look at it. It's complex because it's got headers and encoding and parts. But it's simple, because it's all text. No matter what all of the pieces are, they're all just human readable text. Fortunately, there are many pre-built libraries that help deal with the complexity, allowing you, the script writer, to focus on the task at hand: processing the parts of the message body that you're interested in. Python's "batteries included" philosophy ensures that a good mail processing library ships as part of the core package.

How is any of this Mac-specific? Well, it isn't. Not directly. However, I just mentioned that Python has, by default-no extra installation required-a good e-mail processing library. Python ships standard with OS X. That's part of the equation solved. Then, there's the issue of receiving the mail in the first place.

Just about every contemporary mail system has a method of taking incoming mail and feeding it to a script. Postfix, which ships with OS X, is no exception. By default, an SMTP (Simple Mail Transfer Protocol) server wants to receive mail, decide if the mail is for a valid user on it's system, and to then drop that mail in the user's mailbox. That's it. But what about a list server? Well, you take the same SMTP server, but instead of delivering any mail to an end user's mailbox, you hand all mail off to the list server program. The list server program will determine who to deliver this mail to.

This is also similar to server-side anti-spam. All incoming mail is handed off to an anti-spam program. The mail is analyzed, potentially acted upon (read: dropped), and mail is then fed back into the SMTP server for final delivery.

We're not going to do anything so grand here today, but after finishing up, you'll have the groundwork. If you have an OS X machine acting as a mail relay and really want to test/use this, you're going to need to modify some postfix config files directly.

In /etc/postfix/transport, you'll need to first define a transport. Let's say your main mail server is called mail.example.com. If you want to divert mail to a script, have the mail sent to mproc.example.com, and add the following like to /etc/postfix/transport:

mproc.example.com mproc:

This says, "all mail that arrives for mproc.example.com send it to the transport named mproc." Once a transport is defined, we also need to tell postfix how to connect the dots between the transport named mproc and our script. That happens in /etc/postfix/master.cf. Add the following line to the end of the file:

mproc  unix  -       n       n       -       -       pipe
  flags=DRhu user=mproc argv=/usr/bin/mproc.py

This tells postfix that any mail arriving on the mproc transport should be piped to the mproc.py script. This is, of course, assuming that we store our script in /usr/bin as "mproc.py". Adjust as needed.

Of course, we're going to keep it simple: since the text will be piped into the script, it's easy to simulate. The pipe simply delivers the entire message on stdin.

A Text Processing Script

Again, we said that we're really focusing on processing e-mail as it arrives, so, we're going to look for input via stdin (which the pipe above does for us). Other text processing scripts may want to deal with text already in a file or elsewhere. I'll make sure to cover that in a future column, but that's not the goal of today's exercise. Despite 'keeping it simple,' we'll be covering a few new-to-us concepts.

Here's the assignment: currently, stock information arrives via e-mail where a dedicated person reads the mail and inputs the entries into a database. This person could clearly be doing better things, as this can be automated without changing the backend system that is sending the e-mail message (whether that's a person or a machine is immaterial for this article). These messages will have a strict format: category and value, separated by a colon. The body of a message would look like this:

Company: Cartier

Product: Watch

Model: Original Tank

Number: 12324A332

Price: $4,500

Available: Yes

However, there's a problem when parsing an e-mail message: it's never just the body that you receive. It's headers. And MIME parts. Oy. Fortunately, Python's email library has functions to deal with this.

I say, let's dive right in. Here's the code I'm using, which will be followed by an explanation of the program.

Listing 1: e-mail parsing program, epp.py

#!/usr/bin/env python
import email
import re
import sys
from email.Parser import Parser
# The keywords we're looking for
keys = ['Company', 'Product', 'Model', 'Number', 'Price', 'Available']
# Compile each keyword into a regular expression
keysre = {}
for i in keys:
  keysre[i] = re.compile(i)
# Read stdin into a single string
mystdin = sys.stdin.read()
# Create a parser object and parse the input
p = Parser()
ps = p.parsestr(mystdin)
# Examine each message part for an appripriate plain body
for i in ps.walk():
  if i.get_content_subtype() != "plain":
    continue
  plainbody = i.as_string()
# Break message into lines, based on newline char
plainbody = plainbody.splitlines()
for i in plainbody:
  # Look at each key for a match.
  for k in keys:
    if keysre[k].match(i):
      print i
sys.exit(0)

First thing to notice about the code is the relative brevity-37 lines in total. As usual, the first few lines simply get us set up: she-bang line and relevant imports, including the Python-supplied email module.

#!/usr/bin/env python
import email
import re
import sys
from email.Parser import Parser

There have been a few times in this column that I've mentioned the importance of regular expressions (RE). Python has good support for RE from the re module:

# The keywords we're looking for
keys = ['Company', 'Product', 'Model', 'Number', 'Price', 'Available']
# Compile each keyword into a regular expression
keysre = {}
for i in keys:
  keysre[i] = re.compile(i)

What is happening here is that we define a list of the keywords we're going to be looking for in the message body. Python regular expressions need to be compiled into an object, which is why we define the keysre dictionary. Of course, we could define these objects one at a time, but that's really inelegant and doesn't scale. In the loop, the dictionary is filled with keys that correspond to the words we're going to match, with a value of the compiled RE object.

# Read stdin into a single string
mystdin = sys.stdin.read()
# Create a parser object and parse the input
p = Parser()
ps = p.parsestr(mystdin)

The first part of this section is pretty simple: assign all of stdin to the variable mystdin. Part of the email library is the email parser object. This object allows an e-mail message, headers, MIME parts and all to be parsed, iterated over and picked apart. We're defining a new parser object and then loading the variable ps with a parsed version of the message that's arriving on stdin.

# Examine each message part for an appropriate plain body
for i in ps.walk():
  if i.get_content_subtype() != "plain":
    continue
  plainbody = i.as_string()

This section of the code hands us back the plain part of the message. MIME types are described in two parts, such as "text/html". We're only interested in the plain portion of the message if there are additional parts in the message. The conditional tests if the subpart is not plain. If it is not, we continue and go back to the top of the loop. If it is plain, we fall though and assign the entire subpart, as a string, to the variable plainbody.

# Break message into lines, based on newline char
plainbody = plainbody.splitlines()

The splitlines() string method returns a list, each element a line in the string, split by a separator-by default, the newline character. Now, we can examine each line in turn:

for i in plainbody:
  # Look at each key for a match.
  for k in keys:
    if keysre[k].match(i):
      print i

As we examine each line, an if statement tests for a match of our regular expressions by looping through the keysre dirctionary. If there's a match, we print it out. Naturally, we can take other action here besides printing it out, such as storing it internally, comparing it to some known value or even inserting it into a database. One thing you will likely want to do is to split the matching lines into key/value pairs. The string's split method does this very nicely. For example:

key, value = i.split(':')

The argument to split is the separator to split on. In our case, we know the lines are split by the colon character and that we're expecting back two values. The split method will happily split as many times as needed. In the case where you don't know how many values to expect, you may just want to assign to a list, like so:

values = i.split(':')

From there you can work out how many values were split and returned to you, and what to do with them.

Finally, we exit the program with a 'clean' exit code:

sys.exit(0)

Running the Program

If you don't happen to have any test e-mail sitting around, I've placed one on the MacTech ftp site, under this month's directory (ftp.mactech.com/src/mactech/volume25_2009/25.07.sit ). If you run your own mail server, you can actually just go grab a raw message from the mail spool-your own mail, mind you!

Since the instructions I gave in the first part allow postfix to send incoming mail through a pipe and to the application, we need a more convenient way to test. The command line makes this easy: just pipe it yourself. Don't forget to mark the program as executable:

chmod 770 epp.py

and then pipe away:

cat /path/to/mits_test_mail | ./epp.py

(or, substitute the ./ with the full path to the program, if needed). If you're using the test mail from the MacTech ftp site, you should see the output you expect: the values that we're matching on, with no headers, MIME clutter, etc. Take a look at the original test mail file to see just how much cruft is being left out.

Conclusion

This was a bit of a whirlwind tour of several concepts. I'd encourage you to bulk up an application like this by checking for error conditions and then taking appropriate action. Outside of that, though, it's pretty impressive at how few dedicated commands are needed to process a well-formed e-mail message. The rest are really just 'nuts and bolts' features of the language.

Media of the month: I'd like to think that everyone has some kind of music that they like. Something that reached them, or that reminds them of some period of time. Well, growing up in New York certainly left a musical stamp on me. I just finished "No Wave" by Marc Masters, and I just loved every second of it. I remember the NY scene around that time, but was certainly too young to fully appreciate it. I don't expect everyone to fully enjoy or 'get' No Wave. But sometimes, the best way to enjoy music is by reading about it. So think of the music that inspires you and find the reading material that points out its inspiration. Thanks to Bruce Gerson for inspiring the topic this month.

Next month, we'll expand on some of the concepts covered here and dig deeper into the well that Python has to offer.


Ed Marczak is the Executive Editor of MacTech Magazine. He has written for MacTech since 2004.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Apple Remote Desktop 3.8 - Remotely cont...
Apple Remote Desktop is the best way to manage the Mac computers on your network. Distribute software, provide real-time online help to end users, create detailed software and hardware reports, and... Read more
NeoOffice 2014.7 - Mac-tailored, OpenOff...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
DesktopLyrics 2.6.6 - Displays current i...
DesktopLyrics is an application that displays the lyrics of the song currently playing in "iTunes" right on your desktop. The lyrics for the song have to be set in iTunes; DesktopLyrics does nothing... Read more
Ember 1.8.3 - Versatile digital scrapboo...
Ember (formerly LittleSnapper) is your digital scrapbook of things that inspire you: websites, photos, apps or other things. Just drag in images that you want to keep, organize them into relevant... Read more
Apple iTunes 12.1 - Manage your music, m...
Apple iTunes lets you organize and play digital music and video on your computer. It can automatically download new music, app, and book purchases across all your devices and computers. And it's a... Read more
LibreOffice 4.4.3 - Free, open-source of...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
FoldersSynchronizer 4.2.1 - Synchronize...
FoldersSynchronizer is a popular and useful utility that synchronizes and backs-up files, folders, disks and boot disks. On each session you can apply special options like Timers, Multiple Folders,... Read more
Simon 4.0.2 - Monitor changes and crashe...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
Cocktail 8.1.2 - General maintenance and...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cyberduck 4.6.4 - FTP and SFTP browser....
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more

Playworld Superheroes Review
Playworld Superheroes Review By Tre Lawrence on January 30th, 2015 Our Rating: :: HERO CRAFTINGUniversal App - Designed for iPhone and iPad It’s all about the imagination, fighting bad creatures — and looking good while doing so.   | Read more »
Join the SpongeBob Bubble Party in this...
Join the SpongeBob Bubble Party in this New Match 3 Bubble Poppin’ Frenzy Posted by Jessica Fisher on January 30th, 2015 [ permalink ] | Read more »
Handpick Review
Handpick Review By Jennifer Allen on January 30th, 2015 Our Rating: :: TANTALIZING SUGGESTIONSiPhone App - Designed for the iPhone, compatible with the iPad Handpick will make you hungry, as well as inspire you to cook something... | Read more »
Storm the Halls of Echo Base in First St...
Storm the Halls of Echo Base in First Star Wars: Galactic Defense Event Posted by Jessica Fisher on January 30th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Contradiction Review
Contradiction Review By Tre Lawrence on January 30th, 2015 Our Rating: :: SPOT THE LIEiPad Only App - Designed for the iPad Contradiction is a live action point and click adventure that’s pretty engaging.   Developer: Tim Follin... | Read more »
Unlock Sunshine Girl in Ironkill with th...
Unlock Sunshine Girl in Ironkill with this special 148Apps code Posted by Rob Rich on January 29th, 2015 [ permalink ] Robo-fighter Ironkill has been out on iOS a | Read more »
Crossroad Zombies Review
Crossroad Zombies Review By Jordan Minor on January 29th, 2015 Our Rating: :: CROSSWALKING DEADiPad Only App - Designed for the iPad Crossroad Zombies is a rough draft of a cool genre mash-up.   | Read more »
Blood Brothers 2 – Tips, Cheats, and Str...
War is hell: Is it the kind of hell you want to check out? Read our Blood Brothers 2 review to find out! Blood Brothers 2, DeNA’s follow-up to the original Blood Brothers, is an intriguing card collecting / role-playing / strategy hybrid. There’s... | Read more »
Blood Brothers 2 Review
Blood Brothers 2 Review By Nadia Oxford on January 29th, 2015 Our Rating: :: AN AGGRAVATING RELATIVEUniversal App - Designed for iPhone and iPad Blood Brothers 2 is built on a simple, solid foundation, but its free-to-play system... | Read more »
I AM BREAD, the Toast of the Town, is Ro...
Have you ever dreamt of being deliciously gluten-y? Do you feel passionate about Rye and Wheat? The guys at Bossa Studios do and that is why they are bringing I AM BREAD to iOS soon. The loafy app will feature all the new content that is being... | Read more »

Price Scanner via MacPrices.net

Amazon offers 15-inch 2.2GHz Retina MacBook P...
 Amazon.com has the 15″ 2.2GHz Retina MacBook Pro on sale for $1879 including free shipping. Their price is $120 off MSRP, and it’s the lowest price available for this model from any reseller (except... Read more
Intel Aims to Transform Workplace With 5th-Ge...
Intel Corporation today announced the availability of its 5th generation Intel Core vPro processor family that provides cutting-edge features to enable a new and rapidly shifting workplace. To meet... Read more
iOS App Sharalike Introduces New Instant Smar...
Sharalike slideshow and photo management software for iOS, is making it easier than ever to create shareable meaningful moments with its new instant SmartShow technology. Staying organized is a goal... Read more
Apple Becomes World’s Largest Smartphone Vend...
According to the latest research data from Strategy Analytics, as global smartphone shipments grew 31 percent annually to reach a record 380 million units in the fourth quarter of 2014. Apple became... Read more
Cut the Cord: OtterBox Resurgence Power Case...
Dead batteries and broken phones are two of the biggest issues for smartphone users today. Otterbox addresses both with the new Resurgence Power Case for Apple iPhone 6, promising to make those panic... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $200 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1199.99 save $100 - 13″ 2.6GHz/... Read more
15-inch 2.5GHz Retina MacBook Pro on sale for...
 B&H Photo has the 15″ 2.5GHz Retina MacBook Pro on sale for $2319.99 including free shipping plus NY sales tax only. Their price is $180 off MSRP, and it’s the lowest price available for this... Read more
Back in stock: Refurbished iPod nanos for $99...
The Apple Store has Apple Certified Refurbished 16GB iPod nanos available for $99 including free shipping and Apple’s standard one-year warranty. That’s $50 off the cost of new nanos. Most colors are... Read more
Apple lowers price on refurbished 256GB MacBo...
The Apple Store has lowered prices on Apple Certified Refurbished 2014 MacBook Airs with 256GB SSDs, now available for up to $200 off the cost of new models. An Apple one-year warranty is included... Read more
New Good Management Suite Simplifies Enterpri...
Good Technology has announced the availability of the Good Management Suite, a comprehensive cross-platform solution for organizations getting started with mobile business initiatives. Built on the... Read more

Jobs Board

At-Home Chat Specialist- *Apple* Online Stor...
**Job Summary** At Apple , we believe in hard work, a fun environment, and the kind of creativity and innovation that only comes about when talented people from diverse Read more
Sr. Mac Expert- *Apple* Online Store - Apple...
**Job Summary** The World Wide Apple Online Store (AOS) Sales and Service team is looking for motivated, outgoing, and tech savvy individuals who want to offer Apple Read more
*Apple* Solutions Consultant- Retail Sales (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Event Director, *Apple* Retail Marketing -...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global engagement strategy and team. Delivering an overarching brand Read more
At-Home Chat Specialist- *Apple* Online Stor...
**Job Summary** At Apple , we believe in hard work, a fun environment, and the kind of creativity and innovation that only comes about when talented people from diverse Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.