[SOLVED] How to fix "execution of 'Constant' statements is denied" error?

How to fix "execution of 'Constant' statements is denied" error?

I'm following the tutorial in web.py documentation for templates

    import web
    render = web.template.render('templates')
    print (render.hello('world'))

However when running the python file results in an error :"execution of 'Constant' statements is denied". Google searching doesn't turn up any answers,I need some help please. Thank You

Solution

web.py disallows some types of python legal statements to be executed within the template. I don't know why it's disallowing your particular statement, but there's a way to allow templates to do more:

web/template.py contains a list ALLOWED_AST_NODES which are constructs (used by the abstract syntax tree parser) which are permitted in within templates. You can change that.

In your code, add once:

from web.template import ALLOWED_AST_NODES
ALLOWED_AST_NODES.append('Constant')

Now, this shouldn't be necessary, so I suspect there's something else going on in your code.... mix of versions, perhaps? I believe 'Constant' is a node in python3 AST, but not in python2?

This is a useful technique to add dictionary comprehension .append('DictComp') to the template allowed ast nodes as it already permits list comprehension.