`BUILTINS` is not a valid field name for a frozen dataclass #96151

hauntsaninja · 2022-08-21T07:45:58Z

This is not a bug that I encountered in the wild, but I happened to notice the possibility for this while reading the source.

from dataclasses import dataclass
@dataclass(frozen=True)
class X:
    BUILTINS: str
X(5)

will give you:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 3, in __init__
AttributeError: 'int' object has no attribute 'object'

There are other field names that you can use to trick dataclass into bad behaviour, but all of the other ones are prefixed by an underscore.

So one "fix" is pretty simple: just rename BUILTINS to _BUILTINS in dataclasses.py to bring it in line with the others.

If a single underscore doesn't feel like sufficient "this is the user's fault", we could use __dataclass_* (like we do for __dataclass_self__ param to __init__)

For what it's worth, the only thing we need BUILTINS for is so we can access object inside __init__, so an alternative fix could be to use ().__class__.__base__ instead of BUILTINS.object (and skip the locals dance needed to define BUILTINS altogether)

If any of that sounds worth doing, I'd be happy to open a PR

PR: gh-96151: Use a private name for passing builtins to dataclass #98143

PR: [3.10] gh-96151: Use a private name for passing builtins to dataclass. This now allows for a field named BUILTIN (gh-98143) #98899

PR: [3.11] gh-96151: Use a private name for passing builtins to dataclass. This now allows for a field named BUILTIN (gh-98143) #98900

The text was updated successfully, but these errors were encountered:

There's no indication that BUILTINS is a special name. Other names that are special to dataclass are all prefixed by an underscore. As mentioned in the issue, we can also avoid this locals dance altogether by using `().__class__.__base__` instead of `BUILTINS.object`.

…now allows for a field named BUILTIN (gh-98143)

… This now allows for a field named BUILTIN (pythongh-98143) (cherry picked from commit 29f98b4) Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

…. This now allows for a field named BUILTIN (gh-98143) (gh-98899) gh-96151: Use a private name for passing builtins to dataclass. This now allows for a field named BUILTIN (gh-98143) (cherry picked from commit 29f98b4) Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com> Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

…. This now allows for a field named BUILTIN (gh-98143) (gh-98900) gh-96151: Use a private name for passing builtins to dataclass. This now allows for a field named BUILTIN (gh-98143) (cherry picked from commit 29f98b4) Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com> Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

ericvsmith · 2022-10-31T14:59:51Z

Merge and backports complete. Thanks, @hauntsaninja !

hauntsaninja added the type-bug An unexpected behavior, bug, or error label Aug 21, 2022

hauntsaninja assigned ericvsmith Aug 21, 2022

AlexWaygood added the stdlib Python modules in the Lib dir label Aug 21, 2022

bedevere-bot mentioned this issue Oct 10, 2022

gh-96151: Use a private name for passing builtins to dataclass #98143

Merged

hauntsaninja mentioned this issue Oct 30, 2022

Fields with single underscore names can mess up dataclasses #98886

Open

ericvsmith pushed a commit that referenced this issue Oct 31, 2022

gh-96151: Use a private name for passing builtins to dataclass. This …

29f98b4

…now allows for a field named BUILTIN (gh-98143)

ericvsmith closed this as completed Oct 31, 2022

`BUILTINS` is not a valid field name for a frozen dataclass #96151

`BUILTINS` is not a valid field name for a frozen dataclass #96151

hauntsaninja commented Aug 21, 2022 •

edited by bedevere-bot

ericvsmith commented Oct 31, 2022

BUILTINS is not a valid field name for a frozen dataclass #96151

BUILTINS is not a valid field name for a frozen dataclass #96151

Comments

hauntsaninja commented Aug 21, 2022 • edited by bedevere-bot

ericvsmith commented Oct 31, 2022

`BUILTINS` is not a valid field name for a frozen dataclass #96151

`BUILTINS` is not a valid field name for a frozen dataclass #96151

hauntsaninja commented Aug 21, 2022 •

edited by bedevere-bot