Thinking Notes

More Resources For Twisted Deferreds

2014-12-29T16:30:00-05:00

Twisted Resources

Other Resources

Playing With Twisted and Deferreds And Returning Multiple Arguments

2014-12-28T16:30:00-05:00

Twisted's Deferreds is a cool way of managing callbacks. You can return multiple arguments to the first callback but I wanted to return more than one result for the second function. It occurred to me I should use a tuple. Review the sample below:

    # example.py
from twisted.internet.defer import Deferred

    def myCallback(age, name, sex):
            age += 10
            print age, name, sex
            return (age, name)

    def trueGuy(res):
            print "My full name is", res[1]+' Appleton'
            print "My real age is", res[0]+10

    d = Deferred()
    d.addCallback(myCallback, name='Larry', sex='male')
    d.addCallback(trueGuy)
    d.callback(29)

This bit of code returns a tuple for the first callback. The tuple contains the age and name information for the second callback.

$ python example.py
39 Larry male
My full name is Larry Appleton
My real age is 49

This example works with a tuple. Later I will try and use a dictionary for the same result.

Setting Up A Python Development Environment on Ubuntu 14.04

2014-12-20T16:30:00-05:00

This guide is for me to rmember how I setup a Python development environment on a new machine. These steps were derived from these 2 links:

http://nextdime.wordpress.com/2014/07/03/how-to-set-up-python-development-environment-ubuntu-14-04/

http://www.saltycrane.com/blog/2010/02/how-install-pip-ubuntu/

First, as always, update your sources.

$ sudo apt-get update

Then install the following:

$ sudo apt-get install python-dev
$ sudo apt-get install python-setuptools
$ sudo apt-get install build-essential
$ sudo apt-get install python-pip
$ sudo apt-get install sqlite3

Upgrade pip.

$ sudo pip install --upgrade pip

With pip installed and upgraded, we can now use pip to install virtualenv and the wrapper.

$ sudo pip install virtualenv
$ sudo pip install virtualenvwrapper

Now modify your bashrc file.

if [ -f /usr/local/bin/virtualenvwrapper.sh ]; then
        export WORKON_HOME=$HOME/.virtualenvs
        source /usr/local/bin/virtualenvwrapper.sh
fi

This is a basic python development environment. Please review links above for a more comprehensive setup.

Bash Shell Programming

2014-11-10T18:30:00-05:00

Bash shell programming is still very handy. I will provide a quick summary of commands and constructs.

Assigning a Variable and Printing Out Variable

$ cat=Tom
$ echo $cat
Tom

Reading Input Into A Variable

$ read mouse
Jerry
$ echo $mouse
Jerry

Quoting Affects How Variables Get Printed

$ dog="Thomas"
$ echo "$dog"
dog
$ echo '$dog'
$dog

The IF-THEN-ELIF-THEN-ELSE Conditional

if test -f hello.txt
then
    ...
fi

Also written as:

if [ -f hello.txt ]
then
    ...
fi

For more information, look up the man page for "test"

if condition
then
    ...
elif condition
then
    ...
else
    ...
fi

The FOR Control Structure

for variable in collection
do
    ...
done

for item in 1 2 3
do
    echo $item
done

To be continued...

SPARQL and TWINKLE

2014-11-09T21:34:00-05:00

SPARQL and TWINKLE

The best way to learn SPARQL is by doing it. Twinkle is a great tool you can use to apply SPARQL queries to DBpedia. With Twinkle, we can execute SPARQL queries against DBpedia and local rdf files.

Download zip file.

Do as follows:

unzip twinkle-2.0-bin.zip -d /usr/local/twinkle

add this to your ~/.bash_alias file

alias twinkle="cd /usr/local/twinkle && java -jar twinkle.jar"

The /usr/local/twinkle/example folder has *.rq files containing sample queries.

Fun With Python & AllegroGraph

2013-06-13T20:30:00-04:00

AllegroGraph is a great NoSQL database. Not popular but it provides all the benefits of a database without forcing schema designs on you.

There is a great tutorial on their site.

If you ever used Prolog and remember the relationships and fact building, you can begin to imagine what you can do with AllegroGraph.

Setting Up Bottle with Apache mod_wsgi and virtualenv on Debian

2012-09-16T22:30:00-04:00

Deploying bottle on apache took me some time today which I hope to not repeat. Due to some of my mistakes and errors, I tripped myself up in a mess. I screwed up a new vhost entry on apache because it defaulted back to my default entry. It took me a while to realize I needed a ServerName entry in my new vhost file...

From there I copied some crazy configurations I found through google. They seemed geared towards some other distributions. At the end, I was able to slim my configuration down to several simple files that work.

Lets go over the system I am working on:

debian squeeze - fresh install of 6.0.5
apache - Apache/2.2.16 (Debian) This is the special apache setup
bottle - latest one from github
virtualenv - 1.4.9

First step is first... make sure you can get the default vhost entry operational. I know you want to skip that step, but don't skip it. Sometimes other things break. Make sure you can at least get that setup. Additionally, you should create a second vhost entry with a different ServerName.

The reason you found this article is because you have many projects you want to host on a server. You have different virtual environments for each python project with different libraries. Keeping these projects isolated is a great idea but serving them up isolated is better.

Let's go into the /opt directory as root and create a directory for my user jarvis:

root@palmtree:~$ cd /opt
root@palmtree:/opt$ mkdir jarvis
root@palmtree:/opt$ chown -R jarvis:jarvis jarvis

Let's create the virtualenv in the /opt directory:

jarvis@palmtree:/opt/jarvis$ virtualenv --no-site-packages test
jarvis@palmtree:/opt/jarvis$ cd test
jarvis@palmtree:/opt/jarvis/test$ source bin/activate
jarvis@palmtree:/opt/jarvis/test$ mkdir src
jarvis@palmtree:/opt/jarvis/test$ cd src
jarvis@palmtree:/opt/jarvis/test/src$ touch test.py
jarvis@palmtree:/opt/jarvis/test/src$ touch dispatch.wsgi

Create a test.py file for bottle to run:

from bottle import route, run, request

@route('/', method='GET')
def index1():
    return '<h1>HELLO</h1>'

@route('/hello/:name', method='GET')
def index(name='World'):
    return '<b>Hello %s!</b>' % name

Create a dispatch.wsgi file for apache to run:

import sys, os

# ... build or import your bottle application here ...
import bottle
import test

# Do NOT use bottle.run() with mod_wsgi
application = bottle.default_app()

Go to your apache sites-available directory and copy the default vhost into a new entry:
```
root@palmtree:~# cd /etc/apache2/sites-available/
root@palmtree:~# cp default test
```

Grab your favorite editor and edit the new vhost entry called test:

<VirtualHost *:80>
ServerName test.example.net

WSGIDaemonProcess ptest display-name=%{GROUP}\
 threads=4 \
 python-path=/opt/jarvis/test/src:/opt/jarvis/test/lib/python2.6/site-packages
WSGIProcessGroup ptest
WSGIScriptAlias / /opt/jarvis/test/src/dispatch.wsgi

Alias /robots.txt /opt/jarvis/test/src/apache_static/robots.txt
Alias /favicon.ico /opt/jarvis/test/src/apache_static/favicon.ico

<Directory /opt/jarvis/test/src>
Order allow,deny
Allow from all
</Directory>

ErrorLog ${APACHE_LOG_DIR}/test_error.log

# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn

 CustomLog ${APACHE_LOG_DIR}/test_access.log combined
</VirtualHost>

Activate the conf file, and restart Apache:

root@palmtree:~# a2ensite test
root@palmtree:~# services apache resart

The key to getting this simple configuration to work is in step 6. The line with python-path needs the path to the test.py bottle file and the site-packages directory for the virtualenv that was created. Hopefully this works for you!