Writing Domain Specific Languages with Python

• The process of writing DSL is the same in all languages.
• You write an ideal spec.
• Then, you try to fit the spec so that it's kind of valid syntax for the language you use.
• An example of ideal domain language (well, maybe not so ideal, but quite good):
  

test '/Login':
 GetReq(uname    = 'a_user',
        password = '')
 expect_tmpl:      'login.tmpl'
 expect_tmpl_has:  'errorMsg'
 expect_tmpl_data: { 'uname':'a_user',
                     'missing_fields' : ['Password']}
 expect_session_lacks: 'uid'

• Now the same but as a valid Python syntax:
  

test_serv('/Login',
   GetReq(uname    = 'a_user',
          password = ''),
   expect_tmpl       = 'login.tmpl',
   expect_tmpl_has   = 'errorMsg',
   expect_tmpl_data  = { 'uname':'a_user',
                         'missing_fields' : ['Password']},
   expect_session_lacks = 'uid')

• Useful tricks inclue:
  
• keyword args (expect_tmpl_data=...)
• unbounded arg lists (*args)
• operator overloading __add__(self, other_form)
• reflection via hasattr, getattr, vars and friends
• Thanks to Dan Milstein for his talk at PyCon about Little Languages in Python.
  

IronPython and Windows Forms talk

The presentation in html version

TabbedImages application

• We got some good feedback after the presentation.
• To my surprise there were many people already playing with IronPython.
• What's even more surprising, there were some people that have already used Windows Forms.
• Watch the tabbedimages application, I'm going to extend it with some interesting features.
• If you browse the sources for it, you'll find some simple tests in the MainTest.py.
• They exist because I'm afraid I'm not able to not do Test Driven Development.

PyCon 2007

The PyCon conference is really great.
So far I was at the following talks:

• Internationalization
• Parsing revisited
• Developing desktop applications with Dabo
• I didn't know that creating applications with wxPython is such a pain.
• The Dabo core is simply a layer above the wxPython.
• The application they used on the presentation was an image viewer.
• The API was really nice and in many cases reminded me a simplified version of WinForms API (where you uses strings instead of overused in .Net enumerations).
• wxPython (so Dabo as well) works on all important platforms (Windows, Linux, MacOS)
  

• WSGI - an introduction
• Because there are many different Python web frameworks, WSGI goal is to be able to integrate different layers of different applications.
• I'm still not sure how it could be used in the Ruby world and if there is any need for that.
  
• Writing parsers and compilers with PLY
• Recently, I'm working quite a lot with parsers and PLY is the main tool we use.
• It's very good, very efficient, very elegant
• You declare your grammar rules using docstrings
  
• Creating the WhatWhat project with TurboGears
• WhatWhat is a very simple project tracking tool that was implemented in 4 days using TurboGears.
• It seems that frameworks like TurboGears are becoming quite easy to learn and use.
• Not sure if as easy as Ruby on Rails, though.
  
• I'm still not convinced what could be the reason for me not to use Rails in web applications :)
  
• pyweek: making games in 7 days
• Creating games with Pygame on the GP2X
• SQLAlchemy
• Looks like a very powerful ORM tool for Python.
• Reminds me of Hibernate.
• There is a tool called Elixir which is a layer on top of SQLAlchemy and is more similar to the Ruby ActiveRecord.
• Migrations are only available as extensions.
• However, they are different than Ruby migrations. I didn't quite understand what is really the difference. I was told that Ruby migrations are dangerous because they do too many things for you (!?).
  
• It seems to me the above is one of the fundamental differences between Python and Ruby programmers.
  
• IronPython: Present and future
• That was definitely the best talk so far, IMO.
• Jim is doing a great work in Microsoft.
• My name even appeared at his slide :-)
• He wasn't able to read my name, though ;-)
• What's so difficult with my name? - Andrzej Krzywda
  
• There were screenshots of Michael's tutorial on IronPython and Windows Forms.
• Seo was mentioned, of course. He is the author of FePY - the Comunnity Edition of IronPython.
• The reason of this special edition is that MS can't easily apply patches that are sent by non-MS people.
• IronPython is supported by the MS Robotics project.
• Jim presented a small IP script where he used some MS Gaming API to create a simple 3d game.
• There is a growing support for IronPython in ASP.NET
• Embedding Little Languages in Python
• Little Languages is what the rest of the world calls Domain Specific Languages.
• The talk was about how to use Python to create such a DSL.
• The idea is the same as always with DSL:
• Firstly, you think of an ideal specification.
• You try to use the language features to fit to the spec.
• Python features that are helpful:
• Keyword args
• * args
• getattr, hasattr
• The speaker used _ convention in his code examples.
• I also prefer it, but it doesn't seem to be so popular in the Python community (it is in Ruby community).