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

NTFS 14.3.318 - $19.95
This latest version supports the new macOS 10.12 Sierra! NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and... Read more
iFFmpeg 6.2.2 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
ForeverSave 2.1.6 - Universal auto-save...
ForeverSave auto-saves all documents you're working on while simultaneously doing backup versioning in the background. Lost data can be quickly restored at any time. Define your preferred time... Read more
BetterTouchTool 1.961 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Postbox 5.0.9 - Powerful and flexible em...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
DiskCatalogMaker 6.5.16 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more

Latest Forum Discussions

See All

Enneas Saga lets you lead your own demon...
Defend the land of Enneas Continent from the forces of evil in the new fantasy MMORPG from Lyto Mobi: Enneas Saga. Can’t wait? No problem. It’s available to download now on Android devices. | Read more »
Great zombie games in the spirit of Dead...
Dead Rising 4 arrives tomorrow, giving enthusiasts a fresh chance to take selfies with zombies and get up to other ridiculous end-of-the-world shenanigans. To really get into the spirit of things, we've gone and gathered the best zombie games that... | Read more »
Amateur Surgeon 4 Guide: Advanced tips a...
Amateur Surgeon 4 is still tackling the competition at the top of the App Store charts, so if you haven't tried it out yet, you should probably do that right away. If you've been at it for a while, though, perhaps you're ready to start expanding... | Read more »
Amateur Surgeon 4 Guide: Become the worl...
It's time to wield your trusty pizza cutter again, as Amateur Surgeon has returned with a whole fresh set of challenges (and some old, familiar ones, too). Starting anew isn't easy, especially when all you have at your disposal is a lighter, the... | Read more »
Le Parker: Sous Chef Extraordinaire (Ga...
Le Parker: Sous Chef Extraordinaire 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Telltale Games really is working on a Gu...
Telltale Games' next episodic adventure is indeed Guardians of the Galaxy. A document tied to the voice actors strike suggested that the project was in the work, but now we have direct confirmation following an announcement at the Game Awards that... | Read more »
Amateur Surgeon returns to iOS and Andro...
Amateur Surgeon and its two sequels disappeared from the App Store some time and it was sad days for all. But now, just in time for the holidays, the Adult Swim favorite makes its joyous return in the shape of Amateur Surgeon 4, a remake with... | Read more »
The best board games on mobile
Sometimes you need to ditch all of the high speed, high action games in favor of something a little more traditional. If you don't feel like parting ways from your mobile device, though, there are still plenty of ways to get that old-school fix.... | Read more »
The best Facebook Messenger Instant Game...
Facebook's new Instant Games is now here, meaning you can play games with your friends directly via Facebook. It's a fun new way to connect with friends, of course, but it's also proving to be a solid gaming experience in its own right, with a... | Read more »
You can now play game's on Facebook...
Facebook launched its new Instant Games platform in an exciting new attempt to engage its user base. As a result, you can now play a number of different games directly through Facebook Messenger. All of these games run with HTML5, meaning you play... | Read more »

Price Scanner via MacPrices.net

New 2016 13-inch 2.0GHz MacBook Pros in stock...
Overstock.com has the non-Touch Bar 13″ MacBook Pros in stock today for $150 off MSRP. Shipping is free: - 13″ 2.0GHz MacBook Pro Space Gray (MLL42LL/A): $1349.99 $150 off MSRP - 13″ 2.0GHz MacBook... Read more
15-inch 2.6GHz Silver Touch Bar MacBook Pro o...
Adorama has the new 2016 15″ 2.6GHz Silver Touch Bar MacBook Pro (MLW72LL/A) in stock and available for $2349 including free shipping. Adorama charges sales tax in NY & NJ only. Their price is $... Read more
13-inch MacBook Airs on sale for up to $180 o...
Overstock.com has 13″ MacBook Airs on sale for up to $180 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (MMGF2LL/A): $869.99 $130 off MSRP - 13″ 1.6GHz/256GB MacBook Air (sku... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros (MD101LL/A) available for $829, or $270 off original MSRP. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook... Read more
Monday roundup of Holiday Mac sales: Up to $3...
Take up to $300 off MSRP on the price of a new Apple Mac at B&H Photo today as part of their Holiday sale. Shipping is free, and B&H charges NY sales tax only. Touch Bar MacBook Pros are in... Read more
12-inch WiFi Apple iPad Pros on sale for up t...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for up to $50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP... Read more
9-inch Apple WiFi iPad Pros on sale for $20-$...
B&H Photo has 9.7″ Apple WiFi iPad Pros on sale for $20-$50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 9″ Space Gray 256GB WiFi iPad Pro: $779.95 $20 off MSRP... Read more
Holiday sale: Apple MacBook Airs available fo...
B&H Photo has 13″ MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/128GB MacBook Air (MMGF2LL/A): $899 $100 off MSRP - 13″ 1.6GHz/... Read more
13-inch Silver Touch Bar MacBook Pro in stock...
Amazon has the new 2016 13″ 2.9GHz/256GB Silver Touch Bar MacBook Pro (MLVP2LL/A) in stock today and on sale for $1749 including free shipping. That’s $50 off MSRP, and it’s the lowest price... Read more
Parallels Toolbox 1.3 for Mac Offers 25 Singl...
Parallels has launched Parallels Toolbox 1.3 for Mac, an upgrade that adds five new utilities to the stand-alone application which was released in August and is available exclusively online at http... Read more

Jobs Board

Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 53586123 Pittsburgh, Pennsylvania, United States Posted: Nov. 28, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC Read more
*Apple* Retail - Multiple Positions- Plano,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Kansas...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Chicago...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Hardware Design Validation Engineer - *Apple...
The Apple Watch team is looking for a Hardware Design Validation Engineer. This person will be part of the Apple Watch hardware team with responsibilities for Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.