Merge pull request #9 from llllllllll/wrap-and-unwrap

ENH: py2 compat wrappers

Author: Scott Sanderson

interface/compat.py

@@ -1,3 +1,4 @@
+import functools
 import sys
 from itertools import repeat
 
@@ -6,17 +7,50 @@
 PY2 = version_info.major == 2
 PY3 = version_info.major == 3
 
-if PY2:  # pragma: nocover
+if PY2:  # pragma: nocover-py3
     from funcsigs import signature, Parameter
 
+    @functools.wraps(functools.wraps)
+    def wraps(func, *args, **kwargs):
+        outer_decorator = functools.wraps(func, *args, **kwargs)
+
+        def decorator(f):
+            wrapped = outer_decorator(f)
+            wrapped.__wrapped__ = func
+            return wrapped
+
+        return decorator
+
     def raise_from(e, from_):
         raise e
 
     def viewkeys(d):
         return d.viewkeys()
 
-else:  # pragma: nocover
-    from inspect import signature, Parameter
+    def unwrap(func, stop=None):
+        # NOTE: implementation is taken from CPython/Lib/inspect.py, Python 3.6
+        if stop is None:
+            def _is_wrapper(f):
+                return hasattr(f, '__wrapped__')
+        else:
+            def _is_wrapper(f):
+                return hasattr(f, '__wrapped__') and not stop(f)
+        f = func  # remember the original func for error reporting
+        memo = {id(f)}  # Memoise by id to tolerate non-hashable objects
+        while _is_wrapper(func):
+            func = func.__wrapped__
+            id_func = id(func)
+            if id_func in memo:
+                raise ValueError('wrapper loop when unwrapping {!r}'.format(f))
+            memo.add(id_func)
+        return func
+
+
+else:  # pragma: nocover-py2
+    from inspect import signature, Parameter, unwrap
+
+    wraps = functools.wraps
+
     exec("def raise_from(e, from_):"  # pragma: nocover
          "    raise e from from_")
 

interface/tests/test_interface.py

@@ -1,7 +1,7 @@
 import pytest
 from textwrap import dedent
 
-from ..compat import PY3
+from ..compat import PY3, wraps
 from ..interface import implements, InvalidImplementation, Interface, default
 
 
@@ -672,3 +672,51 @@ def default_classmethod(cls, x):
 
 Consider changing the implementation of default_method or making these attributes part of HasDefault."""  # noqa
     assert second == expected_second
+
+
+def test_wrapped_implementation():
+    class I(Interface):  # pragma: nocover
+        def f(self, a, b, c):
+            pass
+
+    def wrapping_decorator(f):
+        @wraps(f)
+        def inner(*args, **kwargs):  # pragma: nocover
+            pass
+
+        return inner
+
+    class C(implements(I)):  # pragma: nocover
+        @wrapping_decorator
+        def f(self, a, b, c):
+            pass
+
+
+def test_wrapped_implementation_incompatible():
+    class I(Interface):  # pragma: nocover
+        def f(self, a, b, c):
+            pass
+
+    def wrapping_decorator(f):
+        @wraps(f)
+        def inner(*args, **kwargs):  # pragma: nocover
+            pass
+
+        return inner
+
+    with pytest.raises(InvalidImplementation) as e:
+        class C(implements(I)):  # pragma: nocover
+            @wrapping_decorator
+            def f(self, a, b):  # missing ``c``
+                pass
+
+    actual_message = str(e.value)
+    expected_message = dedent(
+        """
+        class C failed to implement interface I:
+
+        The following methods of I were implemented with invalid signatures:
+          - f(self, a, b) != f(self, a, b, c)"""
+    )
+
+    assert actual_message == expected_message

interface/tests/test_utils.py

@@ -1,5 +1,7 @@
 from ..utils import is_a, unique
 
+from ..compat import wraps, unwrap
+
 
 def test_unique():
     assert list(unique(iter([1, 3, 1, 2, 3]))) == [1, 3, 2]
@@ -8,3 +10,14 @@ def test_unique():
 def test_is_a():
     assert is_a(int)(5)
     assert not is_a(str)(5)
+
+
+def test_wrap_and_unwrap():
+    def f(a, b, c):  # pragma: nocover
+        pass
+
+    @wraps(f)
+    def g(*args):  # pragma: nocover
+        pass
+
+    assert unwrap(g) is f

interface/typed_signature.py

@@ -6,7 +6,7 @@
 """
 import types
 
-from .compat import signature
+from .compat import signature, unwrap
 from .default import default
 
 
@@ -48,7 +48,7 @@ def __str__(self):
 BUILTIN_FUNCTION_TYPES = (types.FunctionType, types.BuiltinFunctionType)
 
 
-def extract_func(obj):
+def _inner_extract_func(obj):
     if isinstance(obj, BUILTIN_FUNCTION_TYPES):
         # Fast path, since this is the most likely case.
         return obj
@@ -57,6 +57,10 @@ def extract_func(obj):
     elif isinstance(obj, property):
         return obj.fget
     elif isinstance(obj, default):
-        return extract_func(obj.implementation)
+        return _inner_extract_func(obj.implementation)
     else:
         return obj
+
+
+def extract_func(obj):
+    return unwrap(_inner_extract_func(obj))