Django's template library tags cant use already decorated things like lru_cache because of getfullargspec

[Batuhan Taşkaya]

Django's template library tags cant use already decorated things like lru_cache because of getfullargspec. I have a tag that requires to be lru_cached but i cant use it without an helper.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib64/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/utils/autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 117, in inner_run
    self.check(display_num_errors=True)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/core/management/base.py", line 390, in check
    include_deployment_checks=include_deployment_checks,
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/core/management/base.py", line 377, in _run_checks
    return checks.run_checks(**kwargs)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/core/checks/registry.py", line 72, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/contrib/admin/checks.py", line 79, in check_dependencies
    for engine in engines.all():
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/utils.py", line 90, in all
    return [self[alias] for alias in self]
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/utils.py", line 90, in <listcomp>
    return [self[alias] for alias in self]
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/utils.py", line 81, in __getitem__
    engine = engine_cls(params)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/backends/django.py", line 25, in __init__
    options['libraries'] = self.get_templatetag_libraries(libraries)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/backends/django.py", line 43, in get_templatetag_libraries
    libraries = get_installed_libraries()
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/backends/django.py", line 108, in get_installed_libraries
    for name in get_package_libraries(pkg):
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/backends/django.py", line 121, in get_package_libraries
    module = import_module(entry[1])
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/batuhan/qubic/aspava/social/templatetags/renderer.py", line 25, in <module>
    @lru_cache(None)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/library.py", line 132, in simple_tag
    return dec(func)
  File "/home/batuhan/.local/share/virtualenvs/aspava-SBPNYCrJ/lib/python3.7/site-packages/django/template/library.py", line 109, in dec
    params, varargs, varkw, defaults, kwonly, kwonly_defaults, _ = getfullargspec(func)
  File "/usr/lib64/python3.7/inspect.py", line 1132, in getfullargspec
    raise TypeError('unsupported callable') from ex
TypeError: unsupported callable

It can be solved with unwrapping the function like templates/base.py did.

[Carlton Gibson]

I'm guessing the answer here may well just be "use a helper" — i.e. structure your code so that you can cache the output, but...

There's not enough to go on here. Please show the minimal example that you think should work.

[Simon Charette]

I think the issue is well explained through the PR submitted by the author

​https://github.com/django/django/pull/11334

re-opening.

[Carlton Gibson]

Thanks Simon. Just saw the PR, and came back here to do the same. 👍

[Mariusz Felisiak <felisiak.mariusz@…>]

In 5c192746:

Fixed #30453 -- Fixed crash of simple_tag() and inclusion_tag() when function is wrapped.

getfullargspec() doesn't work with wrapped functions.