GeezerVison is showing github.com — Nested AttributeError improved messages don't work with properties · Issue #146171 · python/cpython
Nested AttributeError improved messages don't work with properties #146171DescriptionThe Python 3.15 improved error message for nested attribute access doesn't seem to work on properties.
Rationale
Take the example from the What's new in Python 3.15 docs:
from dataclasses import dataclass
@dataclass
class Circle:
radius: float
@property
def area(self) -> float:
return pi * self.radius**2
class Container:
def __init__(self, inner: Circle) -> None:
self.inner = inner
circle = Circle(radius=4.0)
container = Container(circle)
print(container.area)Running it with the CPython main branch or Python 3.15.0a1 through Python 3.15.0a7 (with uv) produces the following error:
Traceback (most recent call last):
File "/Users/rodrigogs/Documents/cpython/../tmp/circle.py", line 17, in <module>
print(container.area)
^^^^^^^^^^^^^^
AttributeError: 'Container' object has no attribute 'area'If you remove @property or if you try accessing container.radius instead, you get the respective improved messages:
# After removing `@property` from `area`:
Traceback (most recent call last):
File "/Users/rodrigogs/Documents/cpython/../tmp/circle_no_prop.py", line 16, in <module>
print(container.area)
^^^^^^^^^^^^^^
AttributeError: 'Container' object has no attribute 'area'. Did you mean: 'inner.area'?
# ---
# Accessing `radius` instead of the property `area`:
Traceback (most recent call last):
File "/Users/rodrigogs/Documents/cpython/../tmp/circle_radius.py", line 17, in <module>
print(container.radius)
^^^^^^^^^^^^^^^^
AttributeError: 'Container' object has no attribute 'radius'. Did you mean: 'inner.radius'?Helper scripts for easier testing
circle.py — original example that doesn't work
from dataclasses import dataclass
@dataclass
class Circle:
radius: float
@property
def area(self) -> float:
return pi * self.radius**2
class Container:
def __init__(self, inner: Circle) -> None:
self.inner = inner
circle = Circle(radius=4.0)
container = Container(circle)
print(container.area)
circle_radius.py — accessing radius works
from dataclasses import dataclass
@dataclass
class Circle:
radius: float
@property
def area(self) -> float:
return pi * self.radius**2
class Container:
def __init__(self, inner: Circle) -> None:
self.inner = inner
circle = Circle(radius=4.0)
container = Container(circle)
print(container.radius)
circle_no_prop.py — removing the property works
from dataclasses import dataclass
@dataclass
class Circle:
radius: float
# @property
def area(self) -> float:
return pi * self.radius**2
class Container:
def __init__(self, inner: Circle) -> None:
self.inner = inner
circle = Circle(radius=4.0)
container = Container(circle)
print(container.area)
CPython versions tested on:
3.15, CPython main branch
Operating systems tested on:
macOS
Linked PRs
Activityhugovk commented on Mar 19, 2026 okiemute04 commented on Mar 19, 2026 @rodrigogiraoserrao just analyzed the issue. The problem is that the nested attribute suggestion system doesn't understand properties. My proposed solution is to enhance the error suggestion algorithm to recognize property descriptors and examine their getter functions when generating suggestions. This would maintain the existing behavior for regular attributes while adding property support. What do you think? Any suggestions or options that will be a good fit for this issue? pablogsal commented on Mar 20, 2026
@rodrigogiraoserrao just analyzed the issue. The problem is that the nested attribute suggestion system doesn't understand properties. My proposed solution is to enhance the error suggestion algorithm to recognize property descriptors and examine their getter functions when generating suggestions. This would maintain the existing behavior for regular attributes while adding property support. What do you think? Any suggestions or options that will be a good fit for this issue?
Sorry, I didn't read this message earlier.
I ended up taking a slightly different approach from examining the getter function directly. The fix uses static attribute lookup for nested suggestions, so property-backed attributes can be suggested without executing the property getter. That keeps the existing behavior for regular attributes and avoids triggering arbitrary code while formatting the error.
If you want to help, reviewing the change and testing a few edge cases would be useful! pablogsal commented on Mar 20, 2026 Reacted by Hugo van Kemenade Reacted by Rodrigo Girão Serrão okiemute04 commented on Mar 20, 2026 @pablogsal I tested this PR locally with the property example from #146171 and confirmed:
✅ The property getter is not executed (no side effects)
✅ The tests test_getattr_nested_with_property passed and are working as they should
✅ The error message correctly suggests inner.computed for the property-backed attribute
Great work !!!!!!!!!! Reacted by Pablo Galindo Salgado pablogsal commented on Mar 20, 2026 Reacted by Okiemute Enato rodrigogiraoserrao commented on Mar 20, 2026 ContributorAuthor More actions Well, that was quick. 👀 Thanks to both! Reacted by Hugo van Kemenade
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