Tinche · Tinche · May 13, 2024 · May 13, 2024
diff --git a/README.md b/README.md
@@ -51,9 +51,15 @@ wrapping("a string")  # No type error, blows up at runtime.
 
 ## Changelog
 
+### 24.3.0 (UNRELEASED)
+
+- Fix wrapping unannotated functions.
+  ([#2](https://github.com/Tinche/tightwrap/issues/2) [#3](https://github.com/Tinche/tightwrap/pull/3))
+
 ### 24.2.0 (2024-05-04)
 
 - Add support for Python 3.8 and 3.9.
+  ([#1](https://github.com/Tinche/tightwrap/pull/1))
 
 ### 24.1.0 (2024-01-09)
 

diff --git a/pdm.lock b/pdm.lock
diff --git a/src/tightwrap/__init__.py b/src/tightwrap/__init__.py
@@ -1,6 +1,6 @@
 import sys
 from functools import wraps as functools_wraps
-from inspect import Signature
+from inspect import Signature, _empty
 from typing import Any, Callable, TypeVar, cast
 
 from ._backported import eval_if_necessary, get_annotations
@@ -20,12 +20,12 @@ def _get_resolved_signature(fn: Callable[..., Any]) -> Signature:
     evaluated_annotations, fn_globals, fn_locals = get_annotations(fn)
 
     for name, parameter in signature.parameters.items():
-        setattr(parameter, "_annotation", evaluated_annotations[name])
+        parameter._annotation = evaluated_annotations.get(name, _empty)  # type: ignore
 
     new_return_annotation = eval_if_necessary(
         signature.return_annotation, fn_globals, fn_locals
     )
-    setattr(signature, "_return_annotation", new_return_annotation)
+    signature._return_annotation = new_return_annotation  # type: ignore
 
     return signature
 
@@ -42,8 +42,8 @@ def wrapper(fn: Callable[..., R]) -> Callable[P, R]:
         if orig_sig.return_annotation != wrapper_return:
             # We do a little rewriting.
             new_sig = Signature(None, return_annotation=wrapper_return)
-            setattr(new_sig, "_parameters", orig_sig.parameters)
-            setattr(res, "__signature__", new_sig)
+            new_sig._parameters = orig_sig.parameters  # type: ignore
+            res.__signature__ = new_sig  # type: ignore
 
         return cast(Callable[P, R], res)
 

diff --git a/tests/test_wraps.py b/tests/test_wraps.py
@@ -2,8 +2,10 @@
 
 from typing import Any, Callable
 
-from tightwrap import _get_resolved_signature  # pyright: ignore[reportPrivateUsage]
-from tightwrap import wraps
+from tightwrap import (
+    _get_resolved_signature,  # pyright: ignore[reportPrivateUsage]
+    wraps,
+)
 
 
 def test_wraps() -> None:
@@ -39,3 +41,16 @@ def wrapper(*args: Any, **kwargs: Any) -> str:
     assert wrapped_signature.return_annotation is int
 
     _: Callable[[int], str] = wrapper
+
+
+def test_wrap_unannotated() -> None:
+    """Unannotated functions can be wrapped."""
+
+    def inner(a):
+        return a + 1
+
+    @wraps(inner)
+    def outer(*args: Any, **kwargs: Any) -> int:
+        return inner(*args, **kwargs)
+
+    assert outer(3) == 4