8000 gh-102947: Improve traceback when calling `fields()` on a non-dataclass by AlexWaygood · Pull Request #102948 · python/cpython · GitHub
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gh-102947: Improve traceback when calling fields() on a non-dataclass #102948

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Merged
merged 2 commits into from
Mar 23, 2023
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gh-102947: Improve traceback when calling fields() on a non-dataclass #102948

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Improve traceback when calling `fields()` on a non-dataclass
AlexWaygood Mar 23, 2023
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AlexWaygood Mar 23, 2023
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2 changes: 1 addition & 1 deletion Lib/dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1248,7 +1248,7 @@ def fields(class_or_instance):
try:
fields = getattr(class_or_instance, _FIELDS)
except AttributeError:
raise TypeError('must be called with a dataclass type or instance')
raise TypeError('must be called with a dataclass type or instance') from None

# Exclude pseudo-fields. Note that fields is sorted by insertion
# order, so the order of the tuple is as the fields were defined.
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12 changes: 12 additions & 0 deletions Lib/test/test_dataclasses.py
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Expand Up @@ -5,11 +5,13 @@
from dataclasses import *

import abc
import io
import pickle
import inspect
import builtins
import types
import weakref
import traceback
import unittest
from unittest.mock import Mock
from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol, DefaultDict
Expand Down Expand Up @@ -1526,6 +1528,16 @@ class C: pass
with self.assertRaisesRegex(TypeError, 'dataclass type or instance'):
fields(C())

def test_clean_traceback_from_fields_exception(self):
stdout = io.StringIO()
try:
fields(object)
except TypeError as exc:
traceback.print_exception(exc, file=stdout)
printed_traceback = stdout.getvalue()
self.assertNotIn("AttributeError", printed_traceback)
self.assertNotIn("__dataclass_fields__", printed_traceback)

def test_helper_asdict(self):
# Basic tests for asdict(), it should return a new dictionary.
@dataclass
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2023-03-23-13-34-33.gh-issue-102947.cTwcpU.rst
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@@ -0,0 +1,2 @@
Improve traceback when :func:`dataclasses.fields` is called on a
non-dataclass. Patch by Alex Waygood
0