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Fix VariableDoesNotExist exceptions #587

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Fix VariableDoesNotExist exceptions #587

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spiceworm
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These were being thrown if fieldsets and subtitle
are missing from the context.

This commit fixes #586

Fix VariableDoesNotExist exceptions
db25ed3 
These were being thrown if fieldsets and subtitle
are missing from the context.
Mogost
Mogost requested changes Sep 16, 2024
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Django's template processor shouldn't raise an exception if a variable is missing.

@spiceworm
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The exception does not halt execution, but it does appear in the DEBUG logs.

In [1]: from django.http import HttpRequest                                                                                                                       
   ...: from django.template import Template, RequestContext                                                                                                      
   ...:                                                                                                                                                           
   ...: request = HttpRequest()                                                                                                                                   
   ...: request.method = 'GET'                                                                                                                                    
   ...: request.META = {}                                                                                                                                            ...: request.META['SERVER_NAME'] = 'localhost'                                                                                                                 
                                        
In [2]: template = Template("This is a test {{ var_does_not_exist }}")
   ...: context = RequestContext(request)                                                                                                                         
   ...: template.render(context)
DEBUG 2024-09-18 18:46:20,401 base 216 139496148310912 Exception while resolving variable 'var_does_not_exist' in template 'unknown'.
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 883, in _resolve_lookup
    current = current[bit]
              ~~~~~~~^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/template/context.py", line 85, in __getitem__
    raise KeyError(key)
KeyError: 'var_does_not_exist'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 889, in _resolve_lookup
    if isinstance(current, BaseContext) and getattr(
                                            ^^^^^^^^
AttributeError: type object 'RequestContext' has no attribute 'var_does_not_exist'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 899, in _resolve_lookup
    current = current[int(bit)]
                      ^^^^^^^^
ValueError: invalid literal for int() with base 10: 'var_does_not_exist'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 906, in _resolve_lookup
    raise VariableDoesNotExist(
django.template.base.VariableDoesNotExist: Failed lookup for key [var_does_not_exist] in [{'True': True, 'False': False, 'None': None}, {'csrf_token': <SimpleLazy
Object: <function csrf.<locals>._get_val at 0x7edef47f9300>>, 'request': <HttpRequest>, 'user': <django.contrib.auth.models.AnonymousUser object at 0x7edef4307ce0
>, 'perms': PermWrapper(<django.contrib.auth.models.AnonymousUser object at 0x7edef4307ce0>), 'messages': [], 'DEFAULT_MESSAGE_LEVELS': {'DEBUG': 10, 'INFO': 20, 
'SUCCESS': 25, 'WARNING': 30, 'ERROR': 40}}, {}]
Out[2]: 'This is a test '

@spiceworm spiceworm mentioned this pull request Sep 18, 2024
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Mogost commented Sep 18, 2024 •
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The behavior you're showing is typical for Django. If logs are too noisy, you can adjust the logging configuration. Missing context in Django templates is not an issue - {% if something %} works whether the variable exists or not, and both cases are handled safely.

For django-constance, tracking all possible context variables would add unnecessary maintenance overhead.

UPD:
If you insist on merging this PR, then a test is needed to confirm that the problem is fixed on all supported versions and there will be no undetectable regression in the future. But in general, this change seems unnecessary to me.

@camilonova
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I'm closing this. I think it is not necessary.

@camilonova camilonova closed this Oct 28, 2024
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'fieldsets' and 'subtitle' missing from Template context
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@spiceworm @Mogost @camilonova