Merge pull request #186 from apoorvdarshan/fix-138-return-annotation

Fix FunctionMaker.create() with return type annotation (#138)

Author: micheles

CHANGES.md

@@ -3,6 +3,10 @@ HISTORY
 
 ## Unreleased
 
+Fixed `FunctionMaker.create` raising a `SyntaxError` when the signature
+string contains a return annotation, e.g.
+`create("f(a) -> int", "return a")` (issue #138).
+
 ## 5.3.1 (2026-05-18)
 
 Added license SPDX identifier to pyproject.toml (reported by

src/decorator/__init__.py

@@ -253,22 +253,28 @@ def create(cls, obj, body, evaldict, defaults=None,
         attribute __source__ is added to the result. The attributes attrs
         are added, if any.
         """
-        if isinstance(obj, str):  # "name(signature)"
+        if isinstance(obj, str):  # "name(signature)" or "name(signature) -> ret"
             name, rest = obj.strip().split('(', 1)
-            signature = rest[:-1]  # strip a right parens
+            # split the argument list from an optional return annotation;
+            # the argument list ends at the last right parens
+            signature, _, return_annotation = rest.rpartition(')')
             func = None
         else:  # a function
             name = None
             signature = None
+            return_annotation = ''
             func = obj
         self = cls(func, name, signature, defaults, doc, module)
+        self.return_annotation = return_annotation  # e.g. " -> int"
         ibody = '\n'.join('    ' + line for line in body.splitlines())
         caller = evaldict.get('_call_')  # when called from `decorate`
         if caller and iscoroutinefunction(caller):
-            body = ('async def %(name)s(%(signature)s):\n' + ibody)
+            body = ('async def %(name)s(%(signature)s)'
+                    '%(return_annotation)s:\n' + ibody)
             body = re.sub(r'\breturn\b', 'return await', body)
         else:
-            body = 'def %(name)s(%(signature)s):\n' + ibody
+            body = ('def %(name)s(%(signature)s)'
+                    '%(return_annotation)s:\n' + ibody)
         return self.make(body, evaldict, addsource, **attrs)
 
 

tests/test.py

@@ -6,7 +6,7 @@
 import functools
 import asyncio
 from collections import defaultdict, ChainMap, abc as c
-from decorator import dispatch_on, contextmanager, decorator
+from decorator import dispatch_on, contextmanager, decorator, FunctionMaker
 try:
     from . import documentation as doc  # good with pytest
 except ImportError:
@@ -114,6 +114,23 @@ def test_signature(self):
         sig = inspect.signature(doc.f1)
         self.assertEqual(str(sig), '(x)')
 
+    def test_return_annotation(self):
+        # see https://github.com/micheles/decorator/issues/138
+        def add(a, b):
+            return a + b
+
+        # a signature string without a return annotation still works
+        add2 = FunctionMaker.create(
+            'add2(a: int, b: int)', 'return add(a, b)',
+            evaldict={'add': add})
+        self.assertEqual(add2(6, 8), 14)
+
+        # a signature string with a return annotation must not raise
+        add3 = FunctionMaker.create(
+            'add3(a: int, b: int) -> int', 'return add(a, b)',
+            evaldict={'add': add})
+        self.assertEqual(add3(6, 8), 14)
+
     def test_unique_filenames(self):
         @decorator
         def d1(f, *args, **kwargs):