[Twisted-web] Quick Questions about JS mapping in Athena.

kgi iacovou at gmail.com
Thu May 17 10:57:35 EDT 2007

Hi all.

I have a couple of quick questions regarding JS in Athena. At least, they're 
quick to ask; I hope they're also quick to answer.

First of all, it looks like the mapping of package/module to JS source 
file "ought" to be contained in a plugin.

This is described in the Athena page, and (almost) mandated by the fact that 
athena.py's allJavascriptPackages() performs a plugin search like this:

    from nevow import plugins
    d = {}
    for p in plugin.getPlugIns(inevow.IJavascriptPackage, plugins):
    return d

... which uses the fact that a module passed to getPlugins() will use that as 
the search path, so this will in fact search nevow/plugins/, and that's 

However, the story doesn't end there: nevow/plugins/__init__.py contains the 

  __path__ = [os.path.abspath(os.path.join(x, 'nevow', 'plugins')) for x in 

This means that if I look for modules under nevow/plugins, I will magically 
pick up any module that has been put under a nevow/plugins directory in my 

(Innocent onlookers can see the bottom of 
http://docs.python.org/tut/node8.html for the details; I didn't know this was 
possible until I saw this method being mentioned in the twisted plugin docs 
at http://twistedmatrix.com/projects/core/documentation/howto/plugin.html).

Now this is quite clever, but if I've understood the mechanism right, it's not 
necessarily all that handy, because it dictates either the location of 
particular directories within one's project (i.e. my athena code is not at 
the top-level of my code tree, so I'd prefer not to have 'nevow/plugins' at 
the top-level for getPlugins() to pick up via sys.path) or an unnecessary 
entry into sys.path.

So, my questions is: is there a way to register the JS mapping elsewhere? It 
looks like modifying self.jsModules.mapping directly inside the constructor 
of a LivePage might do it, but that feels hacky as heck.

As an aside: I desperately don't want to ruffle any feathers here, but I also 
feel that using the twisted plugins system to store what amounts to a 
dictionary is a bit of a sledgehammer and nut thing. Since the actual 
LiveElement classes don't even live in the same place as the mapping, it's 
not as if the athena.JSPackages are really "plugins", as they only contain 
data, not code. Wouldn't having a "jsFile" attribute directly on the 
LiveElements be more natural, since in any case, the renderer looks up 
the "jsClass" attribute and looks up the corresponding JS file in jsModules? 
Possibly in conjunction with an attribute (allElements?) on LivePage that you 
can set to pre-declare all Elements you intend to use ahead of time so all 
the JS gets included in the page in the same place).

Secondly, what are the requirements on the naming of JS packages? Many of the 
examples use a dotted notation ("Foo.Bar"), but not all. Is there any 
advantage on the JS side to having multiple modules share a top-level module 
name (memory usage, runtime speed)? Are the strings significant at all? As 
far as I can tell, the keys in the jsModules are arbitrary and just need to 
match the jsClass declarations in the LiveElements and the "// import" 
declarations in JS source files. Am I right in believing that there's no 
requirement that they match the class instances actually used in the JS 
source files?

Anyway, that's my two questions and an aside; thanks for your patience, and 
thanks for any help you can afford.



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