An Alternate Explanation of Continuations

What's a continuation?

If you read the Wikipedia item on continuations, make sure you understand the "continuation sandwich" paragraph which is supposed to be the definitive example of what a continuation is. I like to think of it the other way around - with my patent "what a continuation is not" example.

What a continuation is not?

Imagine you have a bookies slip with a four horse accumulator bet (parlay) on it. Your first three horses win and you are in a situation (the state of the bet) where you have a small fortune going onto the last horse. The horse falls.

Now, if the bookies slip had been a continuation it would have maintained the state after the third race and you could have retrieved that state and tried another horse on the last race. But it isn't and you can't, so tough.

Continuations are an important concept in the Nagare Microframework which I'll be looking at next. Continuations allow Nagare to maintain state in an exciting way which may seem unusual to you if you have used some of the other python frameworks like Flask or Bottle or Django.

Good luck fellow travellers.

Top Python Web Frameworks - Today

Every once in a while it's nice to rediscover old friends. Over the last few years I've had a play with quite a few Python Web Frameworks, but one does tend to get a favourite and stick with it. Same as other areas I suppose - cars, dogs, beers, partners... Still, it's good to have a look at what's new and fresh once in a while (my wife doesn't care, but don't tell my dog.)

example of Python language (Photo credit: Wikipedia)

If you look around the internet, there are probably thirty or so Python Web Frameworks around, but not all of them are actively supported. This means that they are likely to be missing functionality in some of the latest latest areas of interest - OAuth2, HTML5 or mobile support for example. Or maybe they just don't make it easy to stuff that you have become used to over the last few years - AJAX or web services maybe.

In my previous post "My Top Ten Python Web Frameworks" from about 18months ago, I gave you my opinion of what was hot, or not, at that time. Some of those seem to have stalled now - Tipfy, GAE framework, Weblayer; while others have appeared or matured - kiss.py, web.py, wheezy.web.

Below is an alphabetic list of the active (updated this year) which I know about. There may be others out there, so please let me know in the comments at the bottom.

• Bottle now on v0.11
• CubicWeb now on v3.15.5
• Django now on v1.4
• Flask now on v0.9
• kiss.py now on v0.4.9
• Nagare now on v0.4.1
• Pyramid now on v1.3
• TurboGears now on v2.2.0
• web.py now on v0.37
• web2py now on v2.2.1
• wheezy.web now on v0.1

In my next few posts I'll be giving you a run down of what state each of them is in and try to give you some idea of how they fit your requirements.

Good luck fellow traveller.

Hosting Domains on Your Domestic Broadband Connection

It's not ideal, but it is possible to host your own domain(s) on your home broadband connection. Find out how.

Hosting on a Budget?

I showed you in my previous last Nginx & uWSGI Living Together in Your Shed how to set up your own Nginx server to serve WSGI applications like Flask, Django, Bottle, Pyramid etc. This allows you to host your own applications on the cheap. All you need is any old server right?

Well sort of. I mean it's cheap enough to buy your own domain name and you probably will want to, but when you are filling in the registration what do you enter when it asks for your DNS servers?

Static IPs can be bought or leased from IP providers and this makes it possible to host your own DNS services. However most of us have dynamic IP addresses at home because our IP providers keep their costs down by buying big blocks of addresses and dynamically allocating us one from the deck each time we need one, and sometimes for their own maintenance reasons too. 

This means your IP address will change from time to time. 

To get around this you can use a dynamic DNS service such as freedns.afraid.org who will point your domain name at your new IP address every time it changes. Cool. Their service is simple, clear and cheap (or even free). I'll let you investigate that yourself, but the main thing is that when you buy your domain name, you need to fill in the DNS bit using the dynamic DNS server names that they provide.

The final thing is: How do you know when your dynamic IP address changes and how do you inform your dynamic DNS service when it happens? Well, for my own purposes I wrote a little script which will do this for you, it checks if your IP has changed and if it has it calls the special callback URL that freedns and others supply you with. 

You can find it here: https://github.com/colwilson/dynamic-dns-updater

Good luck fellow traveller.

Nginx & uWSGI Living Together in Your Shed

Let's assume you have just bought the memorable domain name idrinkink.org and you want to host your lovely web app on that old server in the shed. 

I recently set up both Flask-Ahoy! and Django-Ahoy! on a five year old desktop my daughter was chucking out, so I can guarantee you that this configuration can handle enough traffic to get you going, or to demo products to your customers.

Before we start, I'm assuming you are familiar with python web frameworks (Django, Flask, Bottle etc) and with using virtualenv to segregate your environments. I usually use Flask as my framework of choice, so I'm using their "Hello World" app here.

Let's get started:

Now the contents of those files:

Finally copy the config into place and start the uwsgi daemon and the server up:


This of course is just the basics, but it will hopefully give you a starting point from which you can fiddle to your hearts content.

Good luck fellow traveller.

My Top Ten Python Web Frameworks

An updated version of this article can be found here.

I have recently revisited all of the Python Web Frameworks that I know of and re-evaluated them for use in a new project.

I did this first two or three years years ago and so I imagine I will be biased by the decisions that I made then, so I think it's only fair to say that I started using Django because of it's fantastic documentation and I suppose the helper scripts which help the beginner along. However, all that Convention over configuration stuff can be too much for me sometimes.

I then moved onto Tipfy because it slotted in so easily to Google App Engine which I was using a lot at the time  and the Django framework itself was starting to be more of a hindrance than a help.

One day however I stumbled upon Bottle which was a revelation. Being a micro framework it's explicit. That is if you want to use something, you make up your mind to do so; it's not some cleverness built into the framework over which you have no obvious control. If you want to know how it works, then read the code!

Finally I came to Flask, another micro framework, because I like the way it is based on Werkzeug and other well trusted libraries which gives me a some peace of mind that it is supportable, and secondly because it is also explicit like Bottle.

All that being said, here's my top ten:

1. Flask - small, fast, easy to learn and built on reassuringly supported libraries.
2. Bottle - small, fast and a great tool for learning.
3. Tipfy - built for GAE, easy to pick up and well supported.
4. Django - contains most of what you will ever need to build a website, well documented, but starting to bulge at the wasteline.
5. Pyramid - the successor to Pylons, this one has great docs and great ideas. It is a framework, but you can unpick the bits you don't like.
6. CubicWeb - like Django, Convention over configuration, but nice in some ways. 
7. GAE framework - Simple, built for GAE, and well documented.
8. Web2py - I hate it, but love it. All that framework kinda helps, kinda hinders. Give it a little time and you can definitely pull a website together, it depends on your personality whether or not you go mad first though.
9. Nagare - I admit I haven't built a full system with this one, but I have a feeling I will be soon. I'd rather it was a wee bit more mature though, but the libraries/concepts it's built on is all good stuff.
10. Weblayer - Another micro framework. Some good ideas here, but could do with a little love, If you are a developer looking for a worthwhile project, you should consider lending a hand.

[Please note I am currently updating this article here]

For more information, please read:

• http://wiki.python.org/moin/WebFrameworks
• http://en.wikipedia.org/wiki/Comparison_of_Web_application_frameworks