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Infinite recursion when using with Django SimpleLazyObject #1177
Description
Hi,
I use an object of type django.utils.functional.SimpleLazyObject as a template variable.
When an AttributeError happens in the inner of a lazy object the template rendering falls into infinite recursion.
Expected Behavior
A traceback about the attribute error is displayed.
Actual Behavior
Template rendering falls into infinite recursion.
Minimal Code To Reproduce
from django.utils.functional import SimpleLazyObject
import jinja2
def raises_attribute_error():
raise AttributeError()
template = jinja2.Template('{{ obj.hello.recursion }}')
template.render(obj=SimpleLazyObject(lambda: raises_attribute_error()))Full Traceback
Traceback (most recent call last):
File "main.py", line 10, in <module>
template.render(obj=SimpleLazyObject(lambda: raises_attribute_error()))
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/jinja2/environment.py", line 1090, in render
self.environment.handle_exception()
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/jinja2/environment.py", line 832, in handle_exception
reraise(*rewrite_traceback_stack(source=source))
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/jinja2/_compat.py", line 28, in reraise
raise value.with_traceback(tb)
File "<template>", line 1, in top-level template code
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/jinja2/environment.py", line 471, in getattr
return getattr(obj, attribute)
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/jinja2/runtime.py", line 738, in _undefined_message
object_type_repr(self._undefined_obj),
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/jinja2/utils.py", line 169, in object_type_repr
if obj.__class__.__module__ in ("__builtin__", "builtins"):
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/django/utils/functional.py", line 224, in inner
self._setup()
File "/Users/rkashapov/Library/Python/3.7/lib/python/site-packages/django/utils/functional.py", line 360, in _setup
self._wrapped = self._setupfunc()
File "main.py", line 10, in <lambda>
template.render(obj=SimpleLazyObject(lambda: raises_attribute_error()))
File "main.py", line 6, in raises_attribute_error
raise AttributeError()
RecursionError: maximum recursion depth exceeded while calling a Python objectYour Environment
- Python version: 3.7.3
- Jinja version: 2.11.1
Activity
davidism commentedon Mar 27, 2020
This is due to the way that Jinja variable lookup and undefined handling works. First it tries to get the attribute
hello, which raises an attribute error. Then it tries to treat the variable as a dict key, which also raises an attribute error, so it returns an undefined object. Then it tries to look up the attrributerecursionon the undefined object, which raises an undefined error, which tries to print out some information about the object (obj.__class__.__name__), which raises an attribute error again.In this case, it's possible to fix this by changing the undefined code to use
type(obj)instead.In general, the code you've shown indicates a bad design. Avoid code that could potentially raise an
AttributeErrorin every situation it's used, as that's a recipe for disaster, especially when looking up attributes.rkashapov commentedon Mar 27, 2020
Thanks