Json expression type for Chameleon

json_expression.py

import json
 
from chameleon.zpt.template import (
    PageTemplate,
    PageTemplateFile
)
from chameleon.tales import StructureExpr
from chameleon.utils import unicode_string
from chameleon.astutil import Symbol


class Json(object):

    def __init__(self, value):
        self.json_string = self.transform(value)

    def __str__(self):
        return unicode_string(self.json_string)

    __html__ = __repr__ = __str__

    @classmethod
    def transform(cls, value):
        return json.dumps(value) \
            .replace('\u2028', r'\u2028') \
            .replace('\u2029', r'\u2029') \
            .replace('</', r'\u003c\u002f')


class JsonExpr(StructureExpr):
    wrapper_class = Symbol(Json)


# extend Chameleon
PageTemplate.expression_types['json'] = JsonExpr
PageTemplateFile.expression_types['json'] = JsonExpr