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gh-82129: Improve annotations for make_dataclass() (#133406)

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Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Carl Meyer <carl@oddbird.net>
This commit is contained in:
Jelle Zijlstra 2025-05-05 08:21:32 -07:00 • committed by GitHub
parent 4e498d1e8b
commit bb5ec6ea6e
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3 changed files with 97 additions and 12 deletions
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53
Lib/dataclasses.py
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@ -244,6 +244,10 @@ _ATOMIC_TYPES = frozenset({
property,
})
# Any marker is used in `make_dataclass` to mark unannotated fields as `Any`
# without importing `typing` module.
_ANY_MARKER = object()
class InitVar:
__slots__ = ('type', )
@ -1591,7 +1595,7 @@ def make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True,
for item in fields:
if isinstance(item, str):
name = item
tp = 'typing.Any'
tp = _ANY_MARKER
elif len(item) == 2:
name, tp, = item
elif len(item) == 3:
@ -1610,15 +1614,49 @@ def make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True,
seen.add(name)
annotations[name] = tp
# We initially block the VALUE format, because inside dataclass() we'll
# call get_annotations(), which will try the VALUE format first. If we don't
# block, that means we'd always end up eagerly importing typing here, which
# is what we're trying to avoid.
value_blocked = True
def annotate_method(format):
def get_any():
match format:
case annotationlib.Format.STRING:
return 'typing.Any'
case annotationlib.Format.FORWARDREF:
typing = sys.modules.get("typing")
if typing is None:
return annotationlib.ForwardRef("Any", module="typing")
else:
return typing.Any
case annotationlib.Format.VALUE:
if value_blocked:
raise NotImplementedError
from typing import Any
return Any
case _:
raise NotImplementedError
annos = {
ann: get_any() if t is _ANY_MARKER else t
for ann, t in annotations.items()
}
if format == annotationlib.Format.STRING:
return annotationlib.annotations_to_string(annos)
else:
return annos
# Update 'ns' with the user-supplied namespace plus our calculated values.
def exec_body_callback(ns):
ns.update(namespace)
ns.update(defaults)
ns['__annotations__'] = annotations
# We use `types.new_class()` instead of simply `type()` to allow dynamic creation
# of generic dataclasses.
cls = types.new_class(cls_name, bases, {}, exec_body_callback)
# For now, set annotations including the _ANY_MARKER.
cls.__annotate__ = annotate_method
# For pickling to work, the __module__ variable needs to be set to the frame
# where the dataclass is created.
@ -1634,10 +1672,13 @@ def make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True,
cls.__module__ = module
# Apply the normal provided decorator.
return decorator(cls, init=init, repr=repr, eq=eq, order=order,
unsafe_hash=unsafe_hash, frozen=frozen,
match_args=match_args, kw_only=kw_only, slots=slots,
weakref_slot=weakref_slot)
cls = decorator(cls, init=init, repr=repr, eq=eq, order=order,
unsafe_hash=unsafe_hash, frozen=frozen,
match_args=match_args, kw_only=kw_only, slots=slots,
weakref_slot=weakref_slot)
# Now that the class is ready, allow the VALUE format.
value_blocked = False
return cls
def replace(obj, /, **changes):