Question

I’ve tried several different ways a while ago, each of them gave a different exception, so I gave up and decided to manually write filters when I need them. But I’m missing the native escapejs and other useful but simple filters.

There are several related questions and answers, but as far as I see none of them gives a seamless way to implement this. I guess the main problem is that django filters routines are tied too much to the django environment.

Please answer only if you managed to use built-in django filters in the Appengine SDK environment, from my experience it’s harder compared to a normal environment, as Appengine environment is limited

Answer 1

Template tags in the Django template engine are simple functions that accept values and parameters. They can all be accessed directly in the source code.

This is output from IPython:

In [173]: from django.template.defaultfilters import  date 

In [174]: date??
Type:       function
String Form:<function date at 0xa2935f0>
File:       /usr/local/python/thor/lib/python2.7/site-packages/django/template/defaultfilters.py
Definition: date(value, arg=None)
Source:
@register.filter(expects_localtime=True, is_safe=False)
def date(value, arg=None):
    """Formats a date according to the given format."""
    if not value:
        return u''
    if arg is None:
        arg = settings.DATE_FORMAT
    try:
        return formats.date_format(value, arg)
    except AttributeError:
        try:
            return format(value, arg)
        except AttributeError:
            return ''

Most of the Django-specific magic resides in the decorator (register.filter) and in the way that the language resolves calls when you type {% load <template library> %} in your template. Look for the definitions in <module>.templatetags modules. Built-ins are located in django.template.defaulttags and django.template.defaultfilters.

If Jinja2 has a way to define new template filters (which it probably does), then you could simply wrap handmade template filters to actual Django functions.

So basically, just create Jinja2 filters that point to the actual Django function definitions.

Edit:
If you do not have access to the actual Django functions, just copy-paste the source code and remove or adapt Django-specific stuff.

The escapejs filter is actually a call to this function in django.utils.html:

_base_js_escapes = (
    ('\\', r'\u005C'),
    ('\'', r'\u0027'),
    ('"', r'\u0022'),
    ('>', r'\u003E'),
    ('<', r'\u003C'),
    ('&', r'\u0026'),
    ('=', r'\u003D'),
    ('-', r'\u002D'),
    (';', r'\u003B'),
    (u'\u2028', r'\u2028'),
    (u'\u2029', r'\u2029')
)

# Escape every ASCII character with a value less than 32.
_js_escapes = (_base_js_escapes +
               tuple([('%c' % z, '\\u%04X' % z) for z in range(32)]))

def escapejs(value):
    """Hex encodes characters for use in JavaScript strings."""
    for bad, good in _js_escapes:
        value = mark_safe(force_unicode(value).replace(bad, good))
    return value