How to programmatically get a list of all first-level keys stored in a namespace?

In the process of developing a custom Jinja2 extension (a tag, not a filter), I am finding myself in the situation where I need to extract a list of first-level keys that refer to the runtime values saved in a namespace.

Individual first-level values with known keys are easy to extract from the namespace with a simple Getattr(Name('my_ns_name', 'load'), 'my_key', 'load') node. But how can I get the list of all first-level keys when not known in advance?

I inspected Namespace objects as returned at runtime by a Name('my_ns_name', 'load') node and haven't found any relevant information there. I also feel that the NSRef node type could possibly be a key to the solution, but I still fail to understand its purpose, specially considering how little documented it is. I also thought of using a For node and iterate through some collection returned by one of the nodes.iter_* functions, but that doesn't seem to apply to namespace attributes. So I'm a bit stuck, now...

Here's a condensed version of my attempts so far:

import pprint

from jinja2 import nodes
from jinja2.ext import Extension

class InspectExtension(Extension):

    tags = {"inspect"}

    def __init__(self, environment):
        super().__init__(environment)

    def parse(self, parser):
        lineno = parser.stream.expect("name:inspect").lineno
        expr = parser.parse_expression()
        context = nodes.DerivedContextReference()

        return nodes.Output([
            nodes.Const(expr),                            # Inspect the AST
            nodes.TemplateData('\n'),                     # For a nicer output
            self.call_method("_render", [expr, context])  # Runtime inspection
        ]).set_lineno(lineno)

    def _render(self, value, context):
        result = {
            "class": value.__class__.__name__,
            "attrs": dir(value),
            "context": list(context.get_all().keys())
        }
        return pprint.pformat(result, compact=False)

inspect = InspectExtension

With this template:

<!DOCTYPE html>
<html><body><pre>
    {% set ns = namespace() %}
    {% set ns.test = 'foobar' %}
    {{ ns.test }}
    {% inspect ns %}
</pre></body></html>

Outputs (rendered HTML):

foobar
Getattr(node=Name(name='ns', ctx='load'), attr='test', ctx='load')
{'attrs': ['__class__',
           '__delattr__',
           '__dict__',
           '__dir__',
           '__doc__',
           '__eq__',
           '__format__',
           '__ge__',
           '__getattribute__',
           '__gt__',
           '__hash__',
           '__init__',
           '__init_subclass__',
           '__le__',
           '__lt__',
           '__module__',
           '__ne__',
           '__new__',
           '__reduce__',
           '__reduce_ex__',
           '__repr__',
           '__setattr__',
           '__setitem__',
           '__sizeof__',
           '__str__',
           '__subclasshook__',
           '__weakref__'],
 'class': 'Namespace',
 'context': ['range',
             'dict',
             'lipsum',
             'cycler',
             'joiner',
             'namespace',
             'environ',
             'get_context',
             'request',
             'result',
             'ctx',
             'ns'],
 'value': }

For completeness:

The extension source code is located in ./j2_ext/inspect.py, along with the customary __init__.py which contains a single statement from .inspect import inspect.
Jinja2 engine is called through jinja2-cli, passing the extension name to the --extension argument, as such:

jinja2 --format=json --extension=.j2_ext.inspect /path/to/my_tpl.j2 < my_data.json

Some relevant documentation:

Official Jinja2 documentation: https://jinja.palletsprojects.com/en/stable/extensions/#extension-api
Examples of Jinja2 extensions: https://github.com/topics/jinja2-extension?o=asc&s=stars

Solution

If you read the source code you'll find that the attributes of jinja2.utils.Namespace are stored in the __attrs attribute, a "private" variable prefixed with double underscores that is subject to name mangling, so you would have to access it with the _Namespace prefix instead.

So to obtain a list of all first-level keys stored in the namespace value, evaluate:

list(value._Namespace__attrs)