How I edit Django templates

Every programmer has their favorite editor and mode of working. Some people have more than one. For example, I use Microsoft Visual Studio when editing .NET code, DrScheme for editing Scheme code, and XEmacs for pretty much everything else.

This post is about how I use XEmacs for editing Django template files, in the hopes that others may find this useful.

The "Other" One True Editor

It's rare that people will get passionate about something as pedestrian as a way of editing plain text, but the brief history of the internet is awash with flamewars and heated discussions with titles like "Emacs vs. XEmacs," "Emacs vs vi," and so on. I'm not about to go into the relative merits, but the fact that certain editors pop up time and time again in these debates must mean there is something special about them.

Early on in my college education I started using Emacs because it was all that was available on the school's servers. (Well, that or vi, but vi was and still is black-magic to me.) I got over the learning curve, and now I'm hooked.

At some point, I switched from Emacs to XEmacs, for reasons I can't remember. At the time, it had some feature which was to me essential. That reason no longer applies, but neither have I had a reason to switch back. These tips may apply even if you use GNU Emacs, but they've only been tested in XEmacs.

My current setup is Xemacs 21.4 (patch 20), running on Windows XP. *gasp!* Yes, I use Windows for Django development. Shocking, I know. I have my reasons. In any case, these tips should work equally well with XEmacs on other platforms.

Multiple Major Modes

I won't include a full XEmacs tutorial here, since there is already plenty of info on the web about it. The key point is that there is a "major mode" for each programming environment. There is a Python mode, a Java mode, and so on. Django templates tend to combine more than one language in a file, so that's when the mmm library comes in handy. It stands for "multiple major modes," and it turns out to be just exactly what we need. We can have html-mode for the HTML parts, JavaScript-mode for the JavaScript parts, css-mode for embedded CSS, and python-mode for the Django template filters and tags.

Which HTML mode?

As often happens in the world of Free Software, there are several options to choose from when setting up HTML editing in XEmacs.

• html-mode. This has the fullest support for HTML parsing and validation. The problem is, when dealing with templates, the HTMl will often not validate, so all kinds of error messages show up.
• sgml-mode. This is a more general mode for SGML (of which XML and HTML 4 are subsets).
• xml-mode. SGML mode specialized for XML.
• hm--html-mode. I have no idea what the HM stands for, but this is a lightweight HTML mode, with basic syntax highlighting and indentation.

I use html-mode for full-fledged HTML documents, and hm--html-mode for templates. So that XEMacs can tell the difference, I use the suffix ".tmpl" for template files.

One problem

I did run into some problems getting mmm-mode to work with XEmacs. It turns out the version of mmm-mode that is distributed with the XEmacs package system is ancient - from 2001. I had to download the newer version of mmm-mode and unzip it into my site-packages directory.

How it looks

Here's a screenshot of me editing an example Django template (borrowed from my beta-registration Django app). I've chosen fairly bright colors to make the syntax highlighting more obvious, but that's all customizable. Notice how the Django tags and variables are easy to find in the file. (Click on the image for a larger size.)

My initialization file

Here is the subset of my ~/.xemacs/init.el file dealing with setting up mmm-mode for XEmacs. I hope someone finds this useful. Let me know if you do, or if you encounter problems.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; CSS-Mode
(autoload 'css-mode "css-mode" "Mode for editing CSS files" t)
(add-to-list 'auto-mode-alist '("\\.css\\'" . css-mode))
(setq cssm-indent-function #'cssm-c-style-indenter)
(setq cssm-indent-level '2)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Use hm--html-mode for files that end in .tmpl (Django templates)
(add-to-list 'auto-mode-alist '("\\.tmpl\\'" . hm--html-mode))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Multiple Major Modes.
(require 'mmm-vars)
(require 'mmm-mode)
(require 'mmm-sample)
(setq mmm-global-mode 'maybe)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Custom MMM classes for Django templates
(mmm-add-classes
 '((my-django-expr
    :submode python-mode
    :face mmm-declaration-submode-face
    :front "{%"
    :back "%}"
    :include-front t
    :include-back t)))

(mmm-add-classes
 '((my-django-var
    :submode python
    :face mmm-output-submode-face
    :front "{{"
    :back "}}"
    :include-front t
    :include-back t)))

(mmm-add-mode-ext-class nil "\\.tmpl\\'" 'embedded-css)
(mmm-add-mode-ext-class nil "\\.tmpl\\'" 'my-django-var)
(mmm-add-mode-ext-class nil "\\.tmpl\\'" 'my-django-expr)
(mmm-add-mode-ext-class nil "\\.tmpl\\'" 'html-js)

;; Use different colors for different sub-modes.
(setq mmm-submode-decoration-level 2)
;; Make the code submode a little more readable.
(set-face-background 'mmm-code-submode-face "#EEEEFF")