Exception Handling when using jinja2.DictLoader

[cmason3]

If I use the jinja2.FileSystemLoader and there is an error within my Jinja2 template then the Exception is raised and it reports the file that caused the issue, e.g:

  File "test.j2", line 1, in template
    Test {% x
jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'x'.

However, if I use jinja2.DictLoader then when it raises an Exception it reports the file as <unknown> even though I am passing it the name of a template, e.g:

  File "<unknown>", line 1, in template
jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'x'.

The following code replicates the issue:

#!/usr/bin/env python3

import jinja2, traceback

template = {
  'Default': '{% Test x'
}

try:
  env = jinja2.Environment(loader=jinja2.DictLoader(template))
  rtemplate = env.get_template('Default')
  content = rtemplate.render()

except Exception:
  traceback.print_exc()

The full trackback is as follows:

Traceback (most recent call last):
  File "/home/cmason3/./test.py", line 11, in <module>
    rtemplate = env.get_template('Default')
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/cmason3/bin/python3/lib/python3.11/site-packages/jinja2/environment.py", line 1013, in get_template
    return self._load_template(name, globals)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/cmason3/bin/python3/lib/python3.11/site-packages/jinja2/environment.py", line 972, in _load_template
    template = self.loader.load(self, name, self.make_globals(globals))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/cmason3/bin/python3/lib/python3.11/site-packages/jinja2/loaders.py", line 138, in load
    code = environment.compile(source, name, filename)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/cmason3/bin/python3/lib/python3.11/site-packages/jinja2/environment.py", line 768, in compile
    self.handle_exception(source=source_hint)
  File "/home/cmason3/bin/python3/lib/python3.11/site-packages/jinja2/environment.py", line 939, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "<unknown>", line 1, in template
jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'Test'.

As we are passing the name of the template into get_template() then it knows the name of the template - the same is true if it includes another template from the dict - is it possible to actually report the template name (instead of <unknown> - maybe <actual template name>) when using the DictLoader? When I include multiple templates it gets quite confusing to understand which template the error occurred in - the line numbers seem to be correct once I work out what template it is referring to.

Environment:

• Python version: 3.11.2
• Jinja version: 3.1.4

[davidism]

The value in the traceback is the name of a file, not the name of a template. There's no file backing templates for DictLoader, only template names.

[cmason3]

Is there no way to add the name of the template into the traceback else the user has no idea which one of their templates caused the error?

[cmason3]

If this isn’t the right way - is there currently any way that I can determine what template in the dictionary caused an exception when using a DictLoader?

[cmason3]

It looks like it is available in jinja2.TemplateError.name and the line number in jinja2.TemplateError.lineno - I assume this is stable?

Update: It looks like it can't be relied upon, some Exceptions which fall under TemplateError populate these fields and some don't - I would have expected TemplateNotFound to set name and lineno to the parent template where the include was placed, but name references the name of the included template that doesn't exist and it doesn't set lineno. There are also other exceptions caused by template syntax errors where these values aren't set at all.