Pythonic way of web-programming

Sun Apr 20 05:21:41 EDT 2003

bitbucket at safe-mail.net (poiboy) writes:

>> > Of course you can use template systems. But this is not always a good
>> > economic decision.
>>
>> OK, but can't one use XML/XLST as a sole solution for the view?
>
> I use XSLT [partially] for that reason; it is a general templating solution. 
> The main reason I use XSLT however is because templating is the best (most 
> relevant) excuse I have to keep another X specification in my repetoire.
>
> The primary drawback to XSLT is having to fudge an XML document out of your
> template variables before being able to transform them. If you're retrieving
> data from a native XML source, great, otherwise you need to build an imaginary
> tree and make sure it matches up with the paths in the template.  
>  
> Next, variable representation in the XSL template is likely to take up a whole
> lot more room than a typical {{template_variable}}. Instead of standing out
> nicely against a backdrop of HTML tags, the template variables in XSL have to
> be searched for in small pools of xsl:for-each|value-of|copy-of|... tags and
> select="/path/to/var" attributes (and if you've ever had trouble matching up
> variable names in templates, you'll have a lot of fun with variable paths).
>
> In the amount of time spent figuring out how to ensure unwanted text would
> not appear without running my variable tree through a schema
> (<xsl:template match="text()"/>), I could have implemented five other methods
> to render my page (just guessing).
>
> Neglecting the inherent joy of an education, I believe the cost of using XSLT
> exceeds what benefits it may have (portability, and..) and is likely more
> expensive than successive rewrites with other template systems.

I've always said that humans shouldn't be forced to read/write XML and
that goes for programmers, too.  Writing a programming language in XML
format seems like the perversion of a sadist to me.

I don't care much about XML programming (haven't had a use for it),
but at PyConDC recently I got together with a couple of guys from the
Twisted project who do care, and designed a nice little meta-language
in Python for doing this sort of template processing.  Here's a little
example of it in action:

    template = body[
        table(id="outer", width="100%", height="100%", border="0")[
            tr(valign="bottom")[
                td(id="output", width="75%", valign="top", model="latestOutput")[
                    div(pattern="listItem", view="html")[
                        "Foo"
                    ]
                ],
                td(id="room-contents", valign="bottom")[
                    strong[
                        "Stuff you have"
                    ],
                    div(model="playerInventory", view="List")[

                        # Note programmatic elements
                        if_(not arg1)
                        [    
                            div(_class="item")["Nothing"]
                        ].else_
                        [
                            for_each(arg1)
                            [
                                div(
                                    style=["color: red", "color: blue", None]
                                  , view="item"
                                  , controller="look")[arg1]
                                )
                            ]

                        ]
                    ]
                ]
            ]
        ] 
    ]

    # invoke the template with some data
    template(['foo', 'bar', 'baz', 'another item'])

which generates:

    '''<body>
        <table id="outer" width="100%" height="100%" border="0">
            <tr valign="bottom">
                <td id="output" width="75%" valign="top" model="latestOutput">
                    <div pattern="listItem" view="html">
                        Foo
                    </div>
                </td>
                <td>
                    <strong>Stuff you have</strong>
                    <div model="playerInventory" view="List">
                        <div style="color: red" view="item" controller="look">foo</div>
                        <div style="color: blue" view="item" controller="look">bar</div>
                        <div view="item" controller="look">baz</div>
                        <div style="color: red" view="item" controller="look">another item</div>
                    </div>
                </td>
            </tr>
        </table>
    </body>'''

I really loved this because it was the result of healthy
cross-pollination between the cultures and techniques of two very
different programming communities: Python and C++.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com