Python implementation of HAML

UPDATE Dmsl is an active project on github and I am looking for active developers that can submit any bugs they may come across. I have been using it in production environments for nearly one year as of 12/2011. Refer to the repository README for an in depth look at current development,

So it has been a busy past few days. During which I have written up an implementation of HAML in python. The closest thing I saw to this before was GRHML, whose site seems non-functional and I had a hard time finding information on its status. So without further ado, let me introduce DAML, my HAML implementation.

:title = 'Hello World!'

        %title {title}

        :greeting = lambda x: '%p Hello, {0}'.format(x)


        :items = ['a', 'b', 'c', 'd']

        :def is_last(i):
        :   return len(items) is i+1 and '(class=last)' or ''

        %h2 Loop Method 2 (python list comprehension)
            :['%li{0} {1}'.format(is_last(i), x) for i, x in enumerate(items)]


Ok, now this isn’t all it does but let me talk about a couple things first. For one, this project, as of today, is only 3 or 4 days old. Its hard for me to recall b/c I’ve poured a lot of time into trying to make this run as fast as possible. Today on the other hand has produced a lot of slow downs and hackish code for implementing features like Django code blocks. For you XSL people (which would be me) that means a way to name and call templates from other templates. So anyway, a lot of this code from today (and yesterday) needs some love. With that said, lets go over some differences between HAML and DAML when it comes to marking up HTML.

You’ll notice right away that declaring tags is straight forward and precisely the same. I’ve never actually used HAML so I dont know its exact syntax, but I spent a lot of time perusing the documentation for HAML. Now the actual text processor in DAML is quite fast for building documents. At one point during development, when i was still testing speeds in comparison to HAML, I had results along the lines of 0.21ms processing time for DAML versus 2.4ms processing time for HAML. This was for plain-jane HTML declaration. Lets look at some of that now with DAML.

        %title Good Stuff

        #header Some stuff here
            and indentions of plain text
            will all be part of this div

            .span while this child div whose class="span"
                will be embedded within the above div

            while this text is tailed
            and multilined too

        %p and heres some random content too
            %strong that can be played
            however you like.

        %p one thing worth noting is that new tags
            %strong need
            to be on
            %em new lines
            so keep that in mind.

All of this renders fine of course. But I still have a TODO list for handling stuff unrelated to python expression evaluating. Namely comments, escaping, whitespace control. This is pretty much in line with HAML thus far although I often see blank lines in HAML appended with equals-sign and I cant recall what for. Regardless, the next thing to note is the use of variables. Which loosely follows the string.Formatter (and would fully support it if not for speed issues at the moment, but soon hopefully). Lets go over an example of setting and using variables.

:title = 'Hello World!'
%h1 {title}

Simple, eh? Now here’s the deal. There is a sand-boxed python eval going on. All lines starting with :colons are getting added to an evaluation queue that gets compiled and eval’d. Currently you would tag variables just like using string.Formatter and in the future, this will support all the goodies associated with it. Currently though whats going on is its simply accessing the variable declared (versus string.Formatter being setup with the documents namespace and getting called). Never-the-less, this works fine so far. Lets look at some other things we can do with “:”

:l = []
:for x in range(20):
:    l.append(x)

    :['%p {0}'.format(x+1) for x in l]

Notice first, that you can basically freely declare normal python code blocks. You can also declare functions to make use of as shown with the initial intro document. I would say, ideally, the syntax I would want to go for in the majority of cases is something like (for-loop with plain-text block not yet functional)

    :items = ['a', 'b', 'c', 'd']
    :is_last = lambda i: len(items) is i+1 and '(class=last)' or ''
        :for i, x in enumerate(items):
            %li:is_last(i) {x}

    #div.class(attr=val, attr2=val2) oh and here's this too

So this is something I am working towards, but you can totally declare :func(*args) inline right now and it works. Notice, going back to the plain-text that you can freely declare %tag#id.class(attr=val) in almost any order, the only except is you can not start a line with (attr=val) nor can you declare (attr=val)(attr=val) though the latter may be added. Part of my TODO list is to have the ability to span attributes across multiple lines.

Ill touch on one last bit here, I implemented something similar to django blocks (at its most basic level). Its a wee bit limited until i implement multiline filter options as part of the preprocessor I *just* started working on not but 4 hours ago. But let me show what the final syntax would look like


:block header
    %h1 {title} OVERRIDE!

Now the above doesn’t work until i finish a bit on this preprocessor but to show you how that will work, let me show you how the above does currently work


:block('header\n    %h1 {title} OVERRIDE!')

Now that does work, and as you can see, my preprocessor is basically going to go through for indented portions of text under colon directive calls and push it into the related function thats in the sandboxed globals. This basically means that you can write all sorts of text filters and everything really really easy b/c then back on your end you may have a need to do “blank” with “blah. So..
def my_filter(s):
    s = s.splitlines()
    for x in s:
        pass # do blank with blah
    return s

I’ve basically tried to unify a number of features of HAML here so that anything can be easily overridden or customized and extended. Nothing thats just built-in and untouchable. There’s even more to come surely but I am honestly way burnt out on this.

Let me lastly explain just how FAST this works currently. Now before I went in today/yesterday adding in all these crazy bits and pieces, I grabbed the bench suite from genshi that benchmarks all the most popular python templating engines. I wrote my template to do everything to spec as the others were doing and these were my results.

Mako: 0.38ms
DAML: 0.44ms
Cheetah: 0.66ms
Genshi-Text: 0.96ms

and after that it just trailed off into really big numbers with Genshi coming in at 1.5ms?? and django at 2.4ms?? So this thing has the potential to be FAST. Now since the hackery I’ve pulled in the past number of hours I’ve actually almost doubled my processing time and the above test for DAML now runs at 0.85ms but keep in mind i have done no optimization/refactoring/code-cleanup/obvious-bug-fixes-needed to the codebase i just recently committed. So that portion needs some love and I’d love to get the speed back down to what it was just early yesterday morning.

Now, if your interested in the project, pleeease check it out at github, and play around with it. I’m going to slow my development down to a crawl comparitively as I’m really burnt out. I wont be implementing any new features and I’ll be cleaning up my code base yet again and trying to write beautiful code to everything ive hacked together today/last-nite.

And please feel free to contact me by email or comments or however regarding this project. I would like to get the code cleaned up so that I can collaborate on different things to really bring this project up to par.

Thanks, and enjoy