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One thing that bothers me a lot in stack traces is when they include library code, even standard library, and treat it the same as my code. The least helpful stack trace is one that clutters the actually useful information with frames from the bowels of a dependency I have nothing to do with and that certainly aren't responsible for the problem.
I've found it particularly bad with Python web frameworks. Who wants to debug this:
Traceback (most recent call last):
File "/usr/local/lib/python3.7/site-packages/pydantic/validators.py", line 570, in find_validators
if issubclass(type_, val_type):
TypeError: issubclass() arg 1 must be a class
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.7/site-packages/fastapi/utils.py", line 125, in create_response_field
return response_field(field_info=field_info)
File "/usr/local/lib/python3.7/site-packages/pydantic/fields.py", line 272, in __init__
self.prepare()
File "/usr/local/lib/python3.7/site-packages/pydantic/fields.py", line 370, in prepare
self.populate_validators()
File "/usr/local/lib/python3.7/site-packages/pydantic/fields.py", line 508, in populate_validators
*(get_validators() if get_validators else list(find_validators(self.type_, self.model_config))),
File "/usr/local/lib/python3.7/site-packages/pydantic/validators.py", line 579, in find_validators
raise RuntimeError(f'error checking inheritance of {type_!r} (type: {display_as_type(type_)})')
RuntimeError: error checking inheritance of Header(default='', extra={}) (type: Header)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/bin/uvicorn", line 10, in <module>
sys.exit(main())
File "/usr/local/lib/python3.7/site-packages/click/core.py", line 829, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python3.7/site-packages/click/core.py", line 782, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python3.7/site-packages/click/core.py", line 1066, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python3.7/site-packages/click/core.py", line 610, in invoke
return callback(*args, **kwargs)
File "/usr/local/lib/python3.7/site-packages/uvicorn/main.py", line 331, in main
run(**kwargs)
File "/usr/local/lib/python3.7/site-packages/uvicorn/main.py", line 354, in run
server.run()
File "/usr/local/lib/python3.7/site-packages/uvicorn/main.py", line 382, in run
loop.run_until_complete(self.serve(sockets=sockets))
File "uvloop/loop.pyx", line 1456, in uvloop.loop.Loop.run_until_complete
File "/usr/local/lib/python3.7/site-packages/uvicorn/main.py", line 389, in serve
config.load()
File "/usr/local/lib/python3.7/site-packages/uvicorn/config.py", line 288, in load
self.loaded_app = import_from_string(self.app)
File "/usr/local/lib/python3.7/site-packages/uvicorn/importer.py", line 20, in import_from_string
module = importlib.import_module(module_str)
File "/usr/local/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 "./main.py", line 5, in <module>
import db, comments, users, spem, util
File "./comments.py", line 52, in <module>
env = Depends(env),
File "/usr/local/lib/python3.7/site-packages/fastapi/routing.py", line 539, in decorator
callbacks=callbacks,
File "/usr/local/lib/python3.7/site-packages/fastapi/routing.py", line 479, in add_api_route
callbacks=callbacks,
File "/usr/local/lib/python3.7/site-packages/fastapi/routing.py", line 370, in __init__
self.dependant = get_dependant(path=self.path_format, call=self.endpoint)
File "/usr/local/lib/python3.7/site-packages/fastapi/dependencies/utils.py", line 282, in get_dependant
param=param, default_field_info=params.Query, param_name=param_name
File "/usr/local/lib/python3.7/site-packages/fastapi/dependencies/utils.py", line 376, in get_param_field
field_info=field_info,
File "/usr/local/lib/python3.7/site-packages/fastapi/utils.py", line 130, in create_response_field
f"Invalid args for response field! Hint: check that {type_} is a valid pydantic field type"
fastapi.exceptions.FastAPIError: Invalid args for response field! Hint: check that default='' extra={} is a valid pydantic field type
There are two frames here that are my code, and neither of them is the problem.
If you're interested, the problem was that my route's header paramaters were flagged with type annotations: `x_forwarded_for: Header('')` when it should've been `x_forwarded_for = Header('')`.
In Go, Rust and Julia, stack traces include *even the standard library* by default. Python usually doesn't do that.
I understand that in theory this information *could* be useful (though it's never been to me), but there are better ways to provide information that's only occasionally useful.
A possible objection: how can the language distinguish library code from user code? I think it's fairly straightforward: if it's imported from library search folders, it's library code. If it's imported from places that wouldn't be searched if not for the location of the code being run, it's user code. The person writing the user code is almost never interested in stack frames from libraries.