fix: guard against bare unparameterized dict/list in construct_type and transform

[kiankhooban]

get_args(dict) and get_args(list) return empty tuples when no type parameters are present. Four sites were unconditionally indexing into those tuples, raising ValueError or IndexError when a model field is annotated as a bare dict or list instead of Dict[K, V] or List[T].

Crash sites fixed

src/anthropic/_models.py

• construct_type: _, items_type = get_args(type_) → ValueError on bare dict (issue BUG: construct_type() crashes with ValueError when type_ is a bare dict #1619)
• construct_type: inner_type = args[0] → IndexError on bare list (issue BUG: construct_type() raises IndexError when called with bare unparameterized list #1626)

src/anthropic/_utils/_transform.py

• _transform_recursive (sync): get_args(stripped_type)[1] → IndexError on bare dict (issue IndexError on bare (unparameterized) dict annotation in _transform_recursive #1628)
• _async_transform_recursive: same pattern, same fix

Fix

Guard each index access with a length check and fall back to object when no type args are present — preserving the value as-is, which is the correct behaviour for unparameterized containers.

Reproduction

from anthropic._models import construct_type
construct_type(value={"key": "value"}, type_=dict)  # was: ValueError
construct_type(value=["a", "b"], type_=list)         # was: IndexError

from anthropic._utils._transform import transform
transform({"key": "value"}, dict)                    # was: IndexError

Fixes #1619, #1626, #1628

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates type-transformation utilities to handle unparameterized container annotations (e.g., dict / Dict without type args) more safely by defaulting inner types to object instead of indexing missing get_args() entries.

Changes:

• Guard get_args() indexing for dict value types in recursive transform helpers.
• Guard get_args() indexing for dict/list inner types in construct_type.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/anthropic/_utils/_transform.py	Prevents IndexError when transforming dict-like data against dict annotations without type parameters.
src/anthropic/_models.py	Makes construct_type robust to missing generic args for dict and list annotations by falling back to object.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.