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Snippets by simon

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Multiple inheritance of newforms and modelforms

If you try to use multiple inheritance with a modelform (to mix in some fields from an already existing form class for example) you'll get the following rather terrifying error: > "Error when calling the metaclass bases metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases" The solution is to first create the ModelForm, then create a NEW class that inherits from both the ModelForm and the form you want to mixin, then finally apply the recipe from here: [http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/204197](http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/204197)

  • newforms
  • inheritance
  • modelforms
  • multipleinheritance
  • metaclasses
  • metaclass
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Debug view: show available named URL patterns

Hook the show_url_patterns view function in to your URLconf to get a page which simply lists all of the named URL patterns in your system - useful for if your template developers need a quick reference as to what patterns they can use in the {% url %} tag.

  • urlconf
  • debug
  • debugging
  • urlpatterns
  • documentation
  • docs
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Fire Eagle example: views.py from wikinear.com

The views.py used by [wikinear.com](http://wikinear.com/) - see [http://simonwillison.net/2008/Mar/22/wikinear/](http://simonwillison.net/2008/Mar/22/wikinear/) For a more comprehensive API wrapper for Fire Eagle, take a look at [fireeagle_api.py](http://github.com/SteveMarshall/fire-eagle-python-binding/tree/master/fireeagle_api.py)

  • location
  • fireeagle
  • oauth
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Sign a string using SHA1, then shrink it using url-safe base65

Sometimes it's useful to sign data to ensure the user does not tamper with it - for example, cookies or hidden form variables. SHA1 is cryptographically secure but weighs in at 40 characters, which is pretty long if you're going to be passing the data around in a URL or a cookie. These functions knock an SHA1 hash down to just 27 characters, thanks to a base65 encoding that only uses URL-safe characters (defined as characters which are unmodified by Python's urllib.urlencode function). This compressed hash can then be passed around in cookies or URLs, and uncompressed again when the signature needs to be checked. UPDATE: You probably shouldn't use this; see [http://fi.am/entry/urlsafe-base64-encodingdecoding-in-two-lines/](http://fi.am/entry/urlsafe-base64-encodingdecoding-in-two-lines/) for a smarter approach based on Python's built-in base64 module.

  • security
  • base65
  • signing
  • cookies
  • hashlib
  • hashes
  • sha1
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BritishDateField

The date field in the newforms module includes American style mm/dd/yyyy , which anyone outside the US will recognise as being complete madness. This date field behaves sensibly.

  • newforms
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Partial OpenID provider implementation from idproxy.net

Lots of people have asked me when the [django-openid](http://code.google.com/p/django-openid/) package will provide tools for running an OpenID provider (in addition to an OpenID consumer). The answer is "when it's done", but since it's such a common request I've decided to post some example code to help people who want to work it out for themselves. This is the openidserver.py file from [idproxy.net](http://idproxy.net/). It is **incomplete** - the urlconf, models, templates and some utility functions are not included. In other words, it's useless for anything other than providing a few hints as to how you can go about implementing a provider. Nonetheless, it's better than nothing. I hope this will prove a useful example for people trying to figure out how to best integrate the JanRain Python OpenID library with Django to build an OpenID provider.

  • openid
  • incomplete
  • partial
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module_from_path

I needed to dynamically import a module based on a path to that file on disk, without it necessarily being on the Python Path.

  • import
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Retrieve a list of countries from GeoNames

GeoNames provides a useful data file with information about every country in the world (DjangoPeople uses this). Here's an importer that grabs the file from the web and turns it in to a list of dictionaries.

  • countries
  • geonames
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generateChart() for creating a Google Chart API pie chart from JavaScript

I ended up not needing this (there's a good reason it's in JS and not Python, but most people would probably want to do this server-side instead) but I'm stashing it here in case I need it later. It uses jQuery for the .each() method - which is very easy to replace if you need it to work without that dependency. Usage: var src = generateChart({ "foo": 5, "bar": 3, "baz": 6 });

  • javascript
  • googlechartapi
  • piechart
  • graphs
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Counter model - run multiple persistent counters

Sometimes you just need to count things (or create unique-for-your-application IDs). This model class allows you to run as many persistent counters as you like. Basic usage looks like this: >>> Counter.next() 0 >>> Counter.next() 1L >>> Counter.next() 2L That uses the "default" counter. If you want to create and use a different counter, pass its name as a string as the parameter to the method: >>> Counter.next('hello') 0 >>> Counter.next('hey') 0 >>> Counter.next('hello') 1L >>> Counter.next('hey') 1L >>> Counter.next('hey') 2L You can also get the value as hex (if you want slightly shorter IDs, for use in URLs for example): >>> Counter.next_hex('some-counter-that-is-quite-high') 40e

  • database
  • counters
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