TL;DR

Be careful trying to match word boundaries in Python using regular expressions.  You have to be sure to either escape the match sequence or use raw strings.

Word boundaries

Word boundaries are a great way of performing regular expression searches for whole words while avoiding partial matches.  For instance, a search for the regular expression “the” would match both the word “the” and the start of the word “thesaurus”.

>>> import re
>>> re.match("the", "the")
# matches
>>> re.match("the", "thesaurus")
# matches 

>>> re.match("\bthe\b", "the")
# no match

It turns out that \b is also used as the backspace control sequence.  Thus in order for the regular expression engine to interpret the word boundary correctly, you need to escape the sequence:

>>> re.match("\\bthe\\b", "the")
# match

You can also use raw string literals and avoid the double backslashes:

>>> re.match(r"\bthe\b", "the")
# match

In case you haven’t seen the raw string prefix before, here is the relevant documentation:

PUZZLER: The Perfect Square Dance!

Sally invited 17 guests to a dance party. She assigned each guest a number from 2 to 18, keeping 1 for herself. The sum of each couple’s numbers was a perfect square. What was the number of Sally’s partner?

Puzzler

The fifth in my ongoing series of solving Car Talk Puzzlers with my programming language of choice.  I’m using Python again, just like last time.

There are a few pieces to this.  The first is, how do we generate a list of all possible pairs that match the perfect square constraint?  With list comprehensions and a helper function this is easy.

def perfect_square(n):
  return math.sqrt(n) == int(math.sqrt(n))

# range creates a list that's exclusive of last number.  Thus to go from 1 to n,
# use range(1, n+1)
guests = range(1, num_guests + 1)
# By enforcing the x# a whole bunch of equivalent pairs (e.g. (3,6) and (6,3)).
pairs = [(x,y) for x in guests for y in guests if x<y and perfect_square(x+y)]
>>> guests
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]
>>> pairs
[(1, 3), (1, 8), (1, 15), (2, 7), (2, 14), (3, 6), (3, 13), (4, 5), (4, 12), (5, 11), (6, 10), (7, 9), (7, 18), (8, 17), (9, 16), (10, 15), (11, 14), (12, 13)]

>>> itertools.combinations([1,2,3,4,5], 2)

# This is a sort of generator object which lazily returns the values as needed.
# To force them to all be evaluated at once, to see how this works,
# wrap the call in a list function.
>>>list(itertools.combinations([1,2,3,4,5],2))
[(1, 2), (1, 3), (1, 4), (1, 5), (2, 3), (2, 4), (2, 5), (3, 4), (3, 5), (4, 5)]

This performs exactly as how we would expect.  Note that I want combinations rather than permutations because the order does not matter.

N choose K formula - number of k element combinations from set of n elements

Yeah, I think we can handle checking 48620 combinations.

def flatten(nested):
  """ Flatten one level of nesting.  Returns a generator object
  For instance:
  list(flatten([(1,3),(5,6)])) --> [1,3,5,6] """
  return itertools.chain.from_iterable(nested)

def all_guests_present_once(combination):
  """ Returns whether each guest is present once
  Combination is a list of tuples, e.g. [(1,5),(7,8)]
  """
  flattened = list(flatten(combination))
  return len(set(flattened)) == len(flattened)

>>> all_guests_present_once([(1,3),(4,5)])
True
>>> all_guests_present_once([(1,3),(3,6)])
False

OK we’re ready to throw it all together.

def dance_arrangement(num_guests):
  """
  Returns a valid pairing for all guests if possible, else an empty set
  """
  # Clearly you need an even number of guests to have everyone paired
  if num_guests % 2 == 1:
    return []
  else:
    # range creates a list that's exclusive of last number.  Thus to go from 1 to n,
    # use range(1, n+1)
    guests = range(1, num_guests + 1)
    # By enforcing the x    # a whole bunch of equivalent pairs (e.g. (3,6) and (6,3)).
    pairs = [(x,y) for x in guests for y in guests if x    # brute force search
    all_arrangements = itertools.combinations(pairs, num_guests / 2)
    return filter(all_guests_present_once, all_arrangements)

Running the program with num_guests = 18, we get

[((1, 15), (2, 14), (3, 13), (4, 12), (5, 11), (6, 10), (7, 18), (8, 17), (9, 16))]

8 [((1, 8), (2, 7), (3, 6), (4, 5))]
14 [((1, 8), (2, 14), (3, 13), (4, 12), (5, 11), (6, 10), (7, 9))]
16 [((1, 8), (2, 7), (3, 6), (4, 5), (9, 16), (10, 15), (11, 14), (12, 13))]
18 [((1, 15), (2, 14), (3, 13), (4, 12), (5, 11), (6, 10), (7, 18), (8, 17), (9, 16))]

As you can see, 8, 14, and 16 guests can also be paired up in this way.  Something to keep in mind the next time you are going to have a party.

Gotchas/Workarounds

Mule IDE specific

The Mule IDE is really a misnomer – it’s not a standalone product, but instead an Eclipse plugin. See the installation guide for more information.

XML validation warnings

By default, Eclipse 3.5 will flag all sorts of spurious errors in your XML configuration file. See the blog post for more details, but here’s the short version on how to solve it:

General

These issues exist whether you use the IDE to deploy the app or deploy the app via the command line.

Failure to launch / Timeouts

Mule is configured via XML. You must declare the namespaces and schema locations in order to make use of the built-in Mule constructs. For instance, here’s a snippet of one of my Mule configurations:

<mule xmlns="http://www.mulesoft.org/schema/mule/core"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns:spring="http://www.springframework.org/schema/beans"
      xmlns:vm="http://www.mulesoft.org/schema/mule/vm"
      xmlns:script="http://www.mulesoft.org/schema/mule/scripting"
      xmlns:http="http://www.mulesoft.org/schema/mule/http"
      xmlns:cxf="http://www.mulesoft.org/schema/mule/cxf"
      xmlns:xm="http://www.mulesoft.org/schema/mule/xml"
      xmlns:pattern="http://www.mulesoft.org/schema/mule/pattern"
      xmlns:servlet="http://www.mulesoft.org/schema/mule/servlet"
      xmlns:jetty="http://www.mulesoft.org/schema/mule/jetty"
      xmlns:test="http://www.mulesoft.org/schema/mule/test"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/3.1/mule.xsd
        http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/3.1/mule-http.xsd
        http://www.mulesoft.org/schema/mule/cxf http://www.mulesoft.org/schema/mule/cxf/3.1/mule-cxf.xsd
        http://www.mulesoft.org/schema/mule/scripting http://www.mulesoft.org/schema/mule/scripting/3.1/mule-scripting.xsd
        http://www.mulesoft.org/schema/mule/pattern http://www.mulesoft.org/schema/mule/pattern/3.1/mule-pattern.xsd
        http://www.mulesoft.org/schema/mule/xml http://www.mulesoft.org/schema/mule/xml/3.1/mule-xml.xsd
        http://www.mulesoft.org/schema/mule/vm http://www.mulesoft.org/schema/mule/vm/3.1/mule-vm.xsd
        http://www.mulesoft.org/schema/mule/servlet http://www.mulesoft.org/schema/mule/servlet/3.1/mule-servlet.xsd
        http://www.mulesoft.org/schema/mule/test http://www.mulesoft.org/schema/mule/test/3.1/mule-test.xsd
        http://www.mulesoft.org/schema/mule/jetty http://www.mulesoft.org/schema/mule/jetty/3.1/mule-jetty.xsd"
        >

Make absolutely sure that the version of the xsd that you include matches the major version of mule that you’re using! If you accidentally place a 3.0 instead of a 3.1 in any of those entries, your app will mysteriously fail to launch and you’ll get a stack trace like the following:

INFO  2011-06-09 17:21:20,015 [main] org.mule.MuleServer: Mule Server initializing...
INFO  2011-06-09 17:21:20,298 [main] org.mule.lifecycle.AbstractLifecycleManager: Initialising RegistryBroker
INFO  2011-06-09 17:21:20,355 [main] org.mule.config.spring.MuleApplicationContext: Refreshing org.mule.config.spring.MuleApplicationContext@19bb5c09: startup date [Thu Jun 09 17:21:20 EDT 2011]; root of context hierarchy
WARN  2011-06-09 17:22:36,265 [main] org.springframework.beans.factory.xml.XmlBeanDefinitionReader: Ignored XML validation warning
java.net.ConnectException: Operation timed out
    at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
    at org.apache.xerces.util.ErrorHandlerWrapper.warning(Unknown Source)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
    at org.apache.xerces.impl.xs.traversers.XSDHandler.reportSchemaWarning(Unknown Source)
    at org.apache.xerces.impl.xs.traversers.XSDHandler.getSchemaDocument1(Unknown Source)
    at org.apache.xerces.impl.xs.traversers.XSDHandler.getSchemaDocument(Unknown Source)
    at org.apache.xerces.impl.xs.traversers.XSDHandler.parseSchema(Unknown Source)
    at org.apache.xerces.impl.xs.XMLSchemaLoader.loadSchema(Unknown Source)

Deploying via command line

While it’s nice to be able to use an IDE to develop Mule applications, I prefer to deploy from the command line. This allows me to script the launch of the applications. Furthermore, this approach works in a headless (screenless) remote server, whereas the IDE approach will not. The basic way to deploy an app has changed from Mule 2.2 to Mule 3. It used to be that you would call mule -config /path/to/your/config.xml. Now you move your application to the $MULE_HOME/apps folder and run mule, which in turn will deploy all the apps in the apps folder. This can be very handy, especially when coupled with the Hot Deployment features of Mule; you no longer need to have one terminal per mule app you’re running. From the article, “Mule 3: A New Deployment Model”, here are the ostensible steps you must take to deploy your application in this manner:

• Create a directory under: $MULE_HOME/apps/foo
• Jar custom classes (if any), and put them under: $MULE_HOME/apps/foo/lib
• Put the master Mule config file at: $MULE_HOME/apps/foo/mule-config.xml (note that it has to be named: mule-config.xml
• Start your app with: mule -app foo

While these instructions are correct, there are a lot of gotchas involved. Let me detail them below.

Relative paths

There is often a need to make reference to resources within your configuration file. For instance, you might need to configure an embedded Jetty webserver and tell Jetty where its configuration file is located. When you do this, it’s crucial that you prepend relative paths in the XML configuration file with ${app.home}.

The reason for this is that the current working directory in which you launch the mule process becomes the current working directory for all of your application configuration files. So if you have mule-config.xml in the root of your folder, and conf/jetty.xml in that same folder, then your reference to the jetty.xml should be ${app.home}/conf/jetty.xml. Otherwise, if you just use conf/jetty.xml and launch mule from a folder that’s not the same as the root folder of your application, all of your paths will break.

Property files / Resources

As the step #2 above says, you must jar up all of your compiled classes and include them in the lib folder of your project. If you don’t do this, you’ll get an exception when your component / custom classes are attempted to be instantiated.

What should be emphasized is that all resources that you reference from within your code must end up in the jar as well. By default, that won’t happen. You can use something like the solution presented in Ant Build: copy properties file to jar file to get this to happen.

Unintentional Application Deletion

When you deploy an app by copying a zip or folder into the apps directory and then running mule, Mule will launch it and then create a text file called ‘$APP_NAME-anchor.text’. If you delete this file, Mule will “undeploy this app in a clean way”. What isn’t noted by this is that it will delete the corresponding zip/folder. So be careful not to accidentally delete your whole project. (Not that I did that or anything).

JDBC drivers problems

One nice feature of the hot deploy process is that Mule will automatically load all of the jars in the lib folder and ensure that they’re on the classpath. Unfortunately there is an extremely annoying problem with JDBC drivers, in which they corresponding jar will be loaded correctly, but then will fail to be found at runtime.

At startup:

Loading the following jars:
=============================
file:/opt/local/Mule/mule-standalone-3.1.1/apps/XMLPlayer/lib/mysql-connector-java-5.1.13-bin.jar
=============================
<!-- snip -->
WARN 2011-06-09 15:56:12,130 [http://XMLPlayer].connector.http.mule.default.receiver.2 org.hibernate.cfg.SettingsFactory: Could not obtain connection to query metadata
java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/db

The exact same project works perfectly in the Mule IDE. The only solution I’ve found is to copy the mysql-connector-java-5.1.13-bin.jar into $MULE_HOME/lib/endorsed. There is a similar bug report but it was closed for some reason. It most certainly does not work the way you would intuitively expect.

Conclusion

Mule 3 has many improvements over Mule 2, particular with the introduction of Flows. Unfortunately, deployment is a much tricker problem than it was in Mule 2, and the resources online are woefully inadequate for the task at hand. I hope this blog post helps some poor soul going through the same frustration I went through to get a Mule 3 application deployed.

These config files assume that both jetty.xml and mule-config.xml are located in the same folder, namely conf.

mule-config.xml

<mule xmlns="http://www.mulesoft.org/schema/mule/core"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns:spring="http://www.springframework.org/schema/beans"
      xmlns:http="http://www.mulesoft.org/schema/mule/http"
      xmlns:xm="http://www.mulesoft.org/schema/mule/xml"
      xmlns:jetty="http://www.mulesoft.org/schema/mule/jetty"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/3.1/mule.xsd
        http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/3.1/mule-http.xsd
scripting.xsd
        http://www.mulesoft.org/schema/mule/xml http://www.mulesoft.org/schema/mule/xml/3.1/mule-xml.xsd
        http://www.mulesoft.org/schema/mule/jetty http://www.mulesoft.org/schema/mule/jetty/3.1/mule-jetty.xsd"
        >
        
  <description>
  This configuration uses an embedded Jetty instance to serve static content.
 </description>


  <jetty:connector configFile="${app.home}/conf/jetty.xml" name="jetty_connector" ></jetty:connector>
  <!-- do not use localhost here or you will not be able to access the server except locally.-->
  <jetty:endpoint address="http://0.0.0.0:8080" 
              name="jettyEndpoint" 
              connector-ref="jetty_connector"
              path="/">
            
  </jetty:endpoint> 

  <model name="Jetty">
    <service name="jettyUMO">
      <inbound>
        <jetty:inbound-endpoint ref="jettyEndpoint" /> 
      </inbound>
    </service>
  </model>
</mule>

jetty.xml

Modified from Newbie Guide to Jetty, namely changing class names (the classes in question are bundled with Mule 3.1.1, in the Jar file found in $MULE_HOME/lib/opt/jetty-6.1.26.jar).

<?xml version="1.0"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">

<Configure id="FileServer" class="org.mortbay.jetty.Server">
  <Set name="handler">
    <New class="org.mortbay.jetty.handler.HandlerList">
      <Set name="handlers">
        <Array type="org.mortbay.jetty.Handler">
          <Item>
            <New class="org.mortbay.jetty.handler.ResourceHandler">
              <!--  Jetty 6.1.26, which comes with Mule 3.1, does not have this method --> 
              <!--<Set name="directoriesListed">true</Set>-->
              <Set name="welcomeFiles">
                <Array type="String">
                  <Item>index.html</Item>
                </Array>
              </Set>
              <!-- This folder maps to the root URL configured for this Jetty endpoint.  If I wanted to start serving content from the a folder named "static", I would replace the . with "static".-->
              <Set name="resourceBase">.</Set>
            </New>
          </Item>
          <Item>
            <New class="org.mortbay.jetty.handler.DefaultHandler" />
          </Item>
        </Array>
      </Set>
    </New>
  </Set>
</Configure>

A gist with both of these code snippets can be found here.

Conclusion

With these two configuration files, you can launch an embedded instance of Jetty within your application, and use it to serve static content. Due to a limitation in the version of Jetty 6.1.26 which Mule 3.1.1 comes with, you cannot use the Jetty instance to list the contents of folders; instead the client must know the absolute path to the file. For my purposes this was not a problem.

Just one of the informative graphics from the article

• Part one
• Part two
• Part three

Interestingly enough, Bing changed its mapping visual style to respond to some of the complaints against it.  See O’Beirne’s post on the updates they made.

The entire 41latitude website is excellent, but these articles in particular piqued my interest.  Hopefully you find them similarly enlightening

I was using Hibernate to map my Java classes to MySQL tables and columns.  For most classes, inserts worked perfectly.  For other classes, I’d consistently get errors like

- SQL Error: 1452, SQLState: 23000
- Cannot add or update a child row: a foreign key constraint fails

By running the command

show engine innodb status

in my mysql window, I found following clue:

110520 14:26:09 Transaction:
TRANSACTION 85B76, ACTIVE 0 sec, OS thread id 4530606080 inserting
mysql tables in use 1, locked 1
1 lock struct(s), heap size 376, 0 row lock(s)
MySQL thread id 3, query id 2175 localhost root update
insert into TableName (pk_Pdu) values (10)
Foreign key constraint fails for table `myproj`.`tablename`:
,
  CONSTRAINT `FKEC7DE11817B41BEB` FOREIGN KEY (`pk_Pdu`) REFERENCES `ParentClass` (`pk_Pdu`)
Trying to add to index `PRIMARY` tuple:
DATA TUPLE: 3 fields;
 0: len 8; hex 800000000000000a; asc         ;;
 1: len 6; hex 000000085b76; asc     [v;;
 2: len 7; hex 00000000000000; asc        ;;

But the parent table `myproj`.`ParentClass`
or its .ibd file does not currently exist!

I knew for a fact the table existed; I was able to query it and it showed up fine. Something else must be going on.

I finally stumbled onto the answer by way of a StackOverflow post:

However, I did rename the tables all to lowercase and that did make a difference. A quick search indicates I should maybe setting lower_case_table_names = 1 since I am using InnoDB. On Mac OS/X it is 2 by default (and I failed to mention I’m using a new box which may be why it isn’t working locally).

Sure enough, as soon as I renamed the table names to be all lowercase underscore separated, things worked perfectly. The default naming strategy in Hibernate names the tables in exactly the same way as the class names (e.g. in CamelCase as opposed to lower_case_underscore_separated). Fortunately the designers saw fit to make this naming convention overridable. All I had to do was add one line of code to fix my entire problem:


Configuration config = new Configuration();
// Name tables with lowercase_underscore_separated
config.setNamingStrategy(new ImprovedNamingStrategy());

Thanks to this blog post on ImprovedNamingStrategy for pointing the way. This post also helped me find the problem.

Conclusion

If you’re using Hibernate and a MySQL database running on MacOSX, make sure that your table names are all in lowercase.  This can be accomplished by using the ImprovedNamingStrategy class when configuring Hibernate.

This experience taught me a valuable lesson.  The first is, sometimes a problem can be caused by something that’s not directly your fault per se (i.e. I hadn’t incorrectly structured my Hibernate annotations, as I initially suspected), but rather due some quirk in the operating system or external tools you’re using.  The second is it’s crucial for cross platform libraries like Hibernate to provide the hooks for you to be able to swap out default behavior, precisely to be able to work around problems like these.  Thankfully Hibernate had built in just the hooks I needed to solve the problem.

Mac OSX cannot handle unzipping the file

The solution is to use Springy, a zip utility for Mac (free trial, ~$20 to buy).  It handles the file perfectly:

Open with Springy

Springy handles KMZ fine

Edit: Found an alternative approach here.  Basically, rename the file .rar instead of .zip and the Unix unzip utility can handle it.

I’ve written a script to incorporate this; find it as a gist here.

Visor allows you to pop up your terminal window at any time

After installing it, your terminal hides until being summoned via a keyboard hotkey.  At that point, it pops into view from the top of the screen (though this can be customized if you desire).  I find it really declutters my desktop, as I no longer need to devote screen real estate to the terminal.  Instead, it’s hidden until I need it.

Due to the way it’s packaged (as a SIMBL plugin that modifies the Terminal app itself), it is unobtrusive, incorporating its settings into the Terminal app itself as opposed to requiring a separate app in your dock or quick launch bar.  It’s simple and works flawlessly.  Can’t ask for much more in a piece of free software.

Visor preferences