templates

[has]

Christoph Zwerschke wrote:
> thakadu schrieb:
> > I have used PyMeld (http://www.entrian.com/PyMeld/) which is one of
> > very few that gives a 100% separation of code and presentation, in fact
> > PyMeld is not strictly speaking a template system at all.
>
> Yes, it is more like XIST that I mentioned in another post.
> The reason why this is slower than native templates seems clear: You
> convert the whole page to objects in memory, and then serialize
> everything back to HTML.

PyMeld's not a good example to judge DOM-style templating by: the main
reason it's a poor performer is its implementation is very inefficient.
There's a couple of third-party redesigns kicking about the web if you
want to search for them; I've not tried them myself but I imagine
performance is one of the issues they address.

It is true that DOM-style templating engines will still tend to be a
bit slower at rendering than a macro-style templating engine even when
all else is equal, but that's a price you always pay for choosing a
dynamic over a static approach.

For example, I once did some quick-n-dirty comparisons for my own
HTMLTemplate engine [1] which is fairly well optimised pure Python
code, and reckon its performance on typical insertion and iteration
tasks is maybe 1/2 - 1/3 of Cheetah's. (IIRC, PyMeld ran up to 100x
slower in those particular tests due to its naive algorithms.)

OTOH, you have to remember that HTML rendering is only one small
component in the overall application, so you really have to consider
this against the performance of the rest of the application to know if
a 2-3x difference in rendering speed makes a significant difference or
not. Chances are the biggest bottlenecks will lie elsewhere. Besides,
if pedal-to-the-metal performance is your primary concern, you should
probably be writing everything in C++ anyway.


> If you are only filling in a few words, then
> native templates will be surely much more effective. But if you are
> messing around with the structure of your page, inserting and adding
> elements, then PyMeld will be probably a better way.

I dunno; DOM-style engines work fine even for simple jobs, while the
big macro-style engines can do a lot of fancy stuff too. I think the
major difference is that the DOM-style engines do things much more
simply. For example, HTMLTemplate's codebase, API and documentation are
maybe a tenth the size of Cheetah's. Rather than trying to provide
every possible feature users might ever want themselves (c.f.
Greenspun's Tenth Rule), they keep out of the way as much as possible
and let the original language provide for the user's needs.

HTH

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[1] http://freespace.virgin.net/hamish.sanderson/htmltemplate.html