Fixed @TypeChecked not working with built-in wrappers

Fixes #89.

docs/versionhistory.rst

@@ -7,7 +7,8 @@ This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-v
 
 - Fixed import errors when using the import hook and trying to import a module that has both a
   module docstring and ``__future__`` imports in it
-- Fixed ``AttributeError`` when using @typechecked on a metaclass
+- Fixed ``AttributeError`` when using ``@typechecked`` on a metaclass
+- Fixed ``@typechecked`` compatibility with built-in function wrappers
 
 **2.6.0** (2019-11-06)
 

tests/test_typeguard.py

@@ -2,7 +2,7 @@
 import sys
 import warnings
 from concurrent.futures import ThreadPoolExecutor
-from functools import wraps, partial
+from functools import wraps, partial, lru_cache
 from io import StringIO, BytesIO
 from typing import (
     Any, Callable, Dict, List, Set, Tuple, Union, TypeVar, Sequence, NamedTuple, Iterable,
@@ -947,6 +947,21 @@ def genfunc() -> Generator[int, str, str]:
 
         exc.match('type of return value must be str; got int instead')
 
+    def test_builtin_decorator(self):
+        @typechecked
+        @lru_cache()
+        def func(x: int) -> None:
+            pass
+
+        func(3)
+        func(3)
+        pytest.raises(TypeError, func, 'foo').\
+            match('type of argument "x" must be int; got str instead')
+
+        # Make sure that @lru_cache is still being used
+        cache_info = func.__wrapped__.cache_info()
+        assert cache_info.hits == 1
+
 
 class TestTypeChecker:
     @pytest.fixture

typeguard/__init__.py

@@ -724,12 +724,15 @@ class with this decorator.
 
         return func
 
+    # Find either the first Python wrapper or the actual function
+    python_func = inspect.unwrap(func, stop=lambda f: hasattr(f, '__code__'))
+
     if not getattr(func, '__annotations__', None):
         warn('no type annotations present -- not typechecking {}'.format(function_name(func)))
         return func
 
     def wrapper(*args, **kwargs):
-        memo = _CallMemo(func, args=args, kwargs=kwargs)
+        memo = _CallMemo(python_func, args=args, kwargs=kwargs)
         check_argument_types(memo)
         retval = func(*args, **kwargs)
         check_return_type(retval, memo)
@@ -746,17 +749,17 @@ def wrapper(*args, **kwargs):
         return retval
 
     async def async_wrapper(*args, **kwargs):
-        memo = _CallMemo(func, args=args, kwargs=kwargs)
+        memo = _CallMemo(python_func, args=args, kwargs=kwargs)
         check_argument_types(memo)
         retval = await func(*args, **kwargs)
         check_return_type(retval, memo)
         return retval
 
     if inspect.iscoroutinefunction(func):
-        if func.__code__ is not async_wrapper.__code__:
+        if python_func.__code__ is not async_wrapper.__code__:
             return wraps(func)(async_wrapper)
     else:
-        if func.__code__ is not wrapper.__code__:
+        if python_func.__code__ is not wrapper.__code__:
             return wraps(func)(wrapper)
 
     # the target callable was already wrapped