metaprogramming and politics

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metaprogramming in Python: What CPython, PyPy, Pyramid, pytest and politics have in common …

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Metaprogramming in Python too often revolves around metaclasses, which are just a narrow application of the “meta” idea and not a great one at that. Metaprogramming more generally deals with reasoning about program code, about taking a “meta” stance on it.  A metaprogram takes a program as input, often just partial programs like functions or classes. Here are a few applications of metaprogramming:

  • CPython is a metaprogram written in C. It takes Python program code as input and interprets it, so that it runs at a higher level than C.
  • PyPy is a metaprogramm written in Python. It takes RPython program code as input and generates a C-level metaprogram (the PyPy interpreter) which itself interprets Python programs and takes another meta stance by generating Assembler pieces for parts of the interpreation execution. If you like, PyPy is a metaprogram generating metaprograms whereas CPython and typical compilers like GCC are “just” a metaprogram.
  • Pyramid is a metaprogram that takes view, model definitions and http-handling code as input and executes them, thereby raising code on a higher level to implement the “Pyramid application” language.
  • pytest is a metaprogram written in Python, taking test, fixture and plugin functions as input and executing them in a certain manner, thereby implementing a testing language.
  • metaclasses: in Python they allow to intercept class creation and introspect methods and attributes, amending their behaviour. Because metaclass-code usually executes at import time, it often uses global state for implementing non-trivial meta aspects.

Apart from these concrete examples, language compilers, testing tools and web frameworks all have metaprogramming aspects. Creating big or small “higher” level or domain-specific languages within Python is as a typical example of metaprogramming. Python is actually a great language for metaprogramming although it could be better.

In future blog posts i plan to talk about some good metaprogramming practise, particularly:

  • keep the layers/levels separate by good naming and API design
  • define a concise “language” for the programs you take as input
  • avoid creating global state in your metaprograms (and elsewhere)
    which can easily happen with meta-classes executing at import time

Lastly, i see metaprogramming at work not only when coding in a computer language. Discussing the legal framing for executing programs on the internet is some kind of metaprogramming, especially if you consider licensing and laws as human-interpreted code which affects how programs can be written, constructed and executed. In reverse, web applications increasingly affect how we interact with each other other, thereby implementing rules formerly dealt with in the arena of politics. Therefore, metaprogramming and politics are fundamentally connected topics.

have metafun, i. e. take fun stuff as input to generate more of it :) holger

Written by holger krekel

November 22, 2012 at 3:04 pm

Mobiles, Python, PyPy and the Zone VM

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Next week i am going to OpenBossa, a developer conference organised by Nokia’s research institute INDT in Brazil. It’s about free and open source developments on small internet devices. I’ll be talking about PyPy on Maemo. In a nutshell, last year we made PyPy cross-compile for the Maemo/Linux platform. It turned out to use less RAM than CPython for virtually all Python objects. It also starts new Python processes faster. We have ideas to make it feasible to run hundreds of small isolated python processes on machines like my 190 Euro mobile or even cheaper ones. I’ll post my slides with some more details next week and probably also twitter and blog a bit about my conference experiences.

To be honest, I’ve long ignored developments in the mobile device world. Maybe mostly because I want to interact with people through open and freely available networks. The way in which mobile networks are run for commercial purposes hampered my use of mobiles and my general interest.

But things seem to be changing rapidly. I appreciate that. There are more and more phones who connect both to mobile networks and to WLANs. The sudden possibility to use the internet whereever i have WLAN access opens up the device for me. My small mobile has 128 MByte and a 250 MHZ ARM CPU. It runs Python. I can freely download tools from other people and use them. Or I can hack something up or get in contact with developers. I can use EMail, Internet radio, Twitter or browse the internet to begin with. I find the software generally likeable although a bit shaky to install and control sometimes.

Well, I’d like to change various aspects of the User interface but they are probably quite hard-wired, e.g. text completion. Nevertheless, i am thrilled by the overall technical opportunities. This device could soon operate my working environment (it has a 16 Gig SD-RAM card for 15 Euros) and become a center piece of collaboration and communication. For this i’d like to trust the software and the people behind it. So I look forward to meet up with developers more familiar with mobile worlds. And to hang around Porto de Galinhas which i have been told is a beautiful place.

Of course, I am also curious to present and discuss how PyPy, with some more efforts, could provide a perfectly fitting Pythonic environment for mobiles. My vision is to have a Python environment for driving all technical aspects of the phone and to instantly share scripts and apps with fellows worldwide. All on the basis of a decentral network comprised of devices participating in it. Similar to what Charles Stross describes in his books as the "Zone VM": a distributed virtual machine and environment.

cheers, holger

Written by holger krekel

March 4, 2009 at 8:35 pm

Posted in metaprogramming

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