模板与编码的 HTML

Question

I have a web-app consisting of some html forms for maintaining some tables (SQlite, with CherryPy for web-server stuff). First I did it entirely 'the Python way', and generated html strings via. code, with common headers, footers, etc. defined as functions in a separate module.

I also like the idea of templates, so I tried Jinja2, which I find quite developer-friendly. In the beginning I thought templates were the way to go, but that was when pages were simple. Once .css and .js files were introduced (not necessarily in the same folder as the .html files), and an ever-increasing number of {{...}} variables and {%...%} commands were introduced, things started getting messy at design-time, even though they looked great at run-time. Things got even more difficult when I needed additional javascript in the or sections.

As far as I can see, the main advantages of using templates are: Non-dynamic elements of page can easily be viewed in browser during design. Except for {} placeholders, html is kept separate from python code. If your company has a web-page designer, they can still design without knowing Python.

while some disadvantages are: {{}} delimiters visible when viewed at design-time in browser Associated .css and .js files have to be in same folder to see effects in browser at design-time. Data, variables, lists, etc., must be prepared in advanced and either declared globally or passed as parameters to render() function.

So - when to use 'hard-coded' HTML, and when to use templates? I am not sure of the best way to go, so I would be interested to hear other developers' views.

TIA, Alan

Answer 1

Although I'm not a Python developer, I'll answer here - I believe the idea of using templates is common for PHP and Python.

Using templates has many advantages, like:

• keeping the code clean. Separating the "logic" (controller) code from the presentation (view) is very important. Working on projects that mix HTML / CSS / JS / Python is really hard.
• keeping HTML in separate files doesn't require you to modify the code itself. For example, placing in the controller code (Python code) might require you to put a slash before each " character.
• you can ask your web designer to learn the basics of templates syntax so he's able to help you much without destroying your work on the controller code (which is quite common when a person with no experience in a given language modifies something)

in fact, there are many more advantages, but those are most important for me.

The only disadvantage is that you have to pass parameters to the rendering function ... which doesn't require much of work. Anyway it's much easier than maintaining any project that mixes controller code with view code.

Generally, you should have a look at >MVC pros and cons question< : What is MVC and what are the advantages of it?

Answer 2

The simplest way to solve your static file problem is to use relative paths when referring to them in your html. For example: <img src="static/image.jpg" />

If you're willing to put in a little more work, you can solve all the design-time problems you mentioned by writing a mini-server to display your templates.

1. Maintain a file full of simple data structures containing example values for all your templates.
2. Use a microframework like Werkzeug to serve http on your local machine.
3. Write a root request handler that scans your data structure list or templates directory to produce an index page with links to all your templates.
4. Write a secondary request handler for non-root requests, which renders the requested template with the data structure of the same name.

You can write this tool in a few hours, and it makes template design very convenient. One nice feature of Werkzeug's built-in wsgi server is that it can automatically reload itself when it detects that a file has changed. You can leave your mini-server running while you edit templates and click links on your index page all day.

Answer 3

I would highly recommend using templates. Templates help to encourage a good MVC structure to your application. Python code that emits HTML, IMHO, is wrong. The reason I say that is because Python code should be responsible for doing logic and not have to worry about presentation. Template syntax is usually restrictive enough that you can't really do much logic within the template, but you can do any presentation specific type logic that you may need.

ymmv.

Answer 4

I think that templates are still the best way to separate presentation from business logic. The key is a good templating engine, in particular, one that can make decisions in the template itself. For Python, I've found the Genshi templating engine to be quite good. It's used by the Trac Wiki/Issue tracking system and is quite powerful, while still leaving the templates easy to work with.

For other tasks, I tend to use the BeautifulSoup module. I'll create a simple HTML page, parse it with BeautifulSoup, use the resulting object to add the necessary data, and then write the output to its destination (typically a file for me).

Answer 5

As a Seaside developer, I see no use for templates, if your designer can do css. In practice, I find it impossible to keep templates DRY. Take a look at this question to see the advantages of using code (a DSL) to generate your page. You might be bound by legacy, of course.

Separation of presentation (html) and business logic in web apps does not lead to good modularisation, ie low coupling and high cohesion. That is why separate template systems don't work well.

I just read Jeff Atwoods "What's Wrong With CSS". This again is a problem long solved in the smalltalk world with the Phantasia DSL