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

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Merged
merged 8 commits into from
Oct 31, 2022
Merged

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

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3e03d52
gh-96151: Use a private name for passing builtins to dataclass
hauntsaninja Oct 10, 2022
7f9f91e
📜🤖 Added by blurb_it.
blurb-it[bot] Oct 10, 2022
2d5f290
add a test case
hauntsaninja Oct 11, 2022
d7e8782
separate out test
hauntsaninja Oct 11, 2022
96cc82b
use dunder builtins
hauntsaninja Oct 17, 2022
e7456f8
actually, prefix with __dataclass
hauntsaninja Oct 30, 2022
8f6e968
Remove builtins logic from _create_fn
hauntsaninja Oct 31, 2022
9d44429
also update comment
hauntsaninja Oct 31, 2022
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9 changes: 4 additions & 5 deletions Lib/dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -426,13 +426,11 @@ def wrapper(self):

def _create_fn(name, args, body, *, globals=None, locals=None,
return_type=MISSING):
# Note that we mutate locals when exec() is called. Caller
# beware! The only callers are internal to this module, so no
# Note that we may mutate locals. Callers beware!
# The only callers are internal to this module, so no
# worries about external callers.
if locals is None:
locals = {}
if 'BUILTINS' not in locals:
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I'd suggest using __BUILTINS__ because dunder names are supposed to be reserved for use by the stdlib.

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Before I commit this, I'd like to spend some time researching why this test is even present, instead of just unconditionally assigning to locals. At the very least it could use a comment.

Also, I'm not sure that exposing all of builtins in locals is a good idea, versus just exposing builtins.object.

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@hauntsaninja hauntsaninja Oct 30, 2022 •
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Good catch, looks like the relevant history is:

That is, I think this check was made dead in #9518, but wasn't noticed in that PR

(Also note that the comment at the top of _create_fn is out of date: we do mutate locals, but not via exec)

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@hauntsaninja hauntsaninja Oct 30, 2022 •
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I can do some double checking (locals should all be created within dataclasses.py) and clean that up + change the PR to only pass along object.

(I'll also note that there's still the inscrutable ().__class__.__base__ option on the table, in case we don't want to expose anything at all)

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@hauntsaninja hauntsaninja Oct 31, 2022 •
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Okay, I audited all the call sites, it looks like there is one case where this check is not dead, but it's accidental.

Over here we reuse the same locals dict for two different _create_fn calls:

cpython/Lib/dataclasses.py

Line 619 in 87b5fd9

locals = {'cls': cls,

so the second time round we already have the entry for builtins in the dict. shrug

So my conclusion is:
a) It's safe to remove the check.
b) We should actually go a little further. Since we only need builtins for the frozen init, we should pass that in explicitly when creating __init__ and remove this from _create_fn

I've gone ahead and pushed this change to the PR

locals['BUILTINS'] = builtins
return_annotation = ''
if return_type is not MISSING:
locals['_return_type'] = return_type
Expand Down Expand Up @@ -462,7 +460,7 @@ def _field_assign(frozen, name, value, self_name):
# self_name is what "self" is called in this function: don't
# hard-code "self", since that might be a field name.
if frozen:
return f'BUILTINS.object.__setattr__({self_name},{name!r},{value})'
return f'__dataclass_builtins_object__.__setattr__({self_name},{name!r},{value})'
return f'{self_name}.{name}={value}'


Expand Down Expand Up @@ -569,6 +567,7 @@ def _init_fn(fields, std_fields, kw_only_fields, frozen, has_post_init,
locals.update({
'MISSING': MISSING,
'_HAS_DEFAULT_FACTORY': _HAS_DEFAULT_FACTORY,
'__dataclass_builtins_object__': object,
})

body_lines = []
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8 changes: 8 additions & 0 deletions Lib/test/test_dataclasses.py
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Expand Up @@ -257,6 +257,14 @@ class C:
c = C('foo')
self.assertEqual(c.object, 'foo')

def test_field_named_BUILTINS_frozen(self):
# gh-96151
@dataclass(frozen=True)
class C:
BUILTINS: int
c = C(5)
self.assertEqual(c.BUILTINS, 5)
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Please create a separate function for this, and don't mix it in with existing tests. Maybe test_field_named_BUILTINS or similar.

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Thanks for the review, made the change :-)


def test_field_named_like_builtin(self):
# Attribute names can shadow built-in names
# since code generation is used.
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-10-10-07-07-31.gh-issue-96151.K9fwoq.rst
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@@ -0,0 +1 @@
Allow ``BUILTINS`` to be a valid field name for frozen dataclasses.