Fix builtin Exception type checking.

Closes #1496

Cython/Compiler/Nodes.py

@@ -2129,7 +2129,7 @@ class FuncDefNode(StatNode, BlockNode):
                     typeptr_cname,
                     arg.accept_none,
                     arg.name,
-                    arg.type.is_builtin_type,
+                    arg.type.is_builtin_type and arg.type.require_exact,
                     code.error_goto(arg.pos)))
         else:
             error(arg.pos, "Cannot test type of extern C class without type object name specification")

Cython/Compiler/PyrexTypes.py

@@ -1138,6 +1138,7 @@ class BuiltinObjectType(PyObjectType):
     has_attributes = 1
     base_type = None
     module_name = '__builtin__'
+    require_exact = 1
 
     # fields that let it look like an extension type
     vtabslot_cname = None
@@ -1157,6 +1158,8 @@ class BuiltinObjectType(PyObjectType):
             # Special case the type type, as many C API calls (and other
             # libraries) actually expect a PyTypeObject* for type arguments.
             self.decl_type = objstruct_cname
+        if name == 'Exception':
+            self.require_exact = 0
 
     def set_scope(self, scope):
         self.scope = scope
@@ -1210,13 +1213,15 @@ class BuiltinObjectType(PyObjectType):
             type_check = 'PyString_Check'
         elif type_name == 'basestring':
             type_check = '__Pyx_PyBaseString_Check'
+        elif type_name == 'Exception':
+            type_check = '__Pyx_PyException_Check'
         elif type_name == 'bytearray':
             type_check = 'PyByteArray_Check'
         elif type_name == 'frozenset':
             type_check = 'PyFrozenSet_Check'
         else:
             type_check = 'Py%s_Check' % type_name.capitalize()
-        if exact and type_name not in ('bool', 'slice'):
+        if exact and type_name not in ('bool', 'slice', 'Exception'):
             type_check += 'Exact'
         return type_check
 

Cython/Utility/ModuleSetupCode.c

@@ -308,6 +308,7 @@
 #endif
 
 #define __Pyx_TypeCheck(obj, type) PyObject_TypeCheck(obj, (PyTypeObject *)type)
+#define __Pyx_PyException_Check(obj) __Pyx_TypeCheck(obj, PyExc_Exception)
 
 #if PY_MAJOR_VERSION >= 3
   #define PyIntObject                  PyLongObject

tests/run/builtin_type_inheritance_T608.pyx

@@ -125,3 +125,26 @@ cdef class MyException(Exception):
     cdef readonly int value
     def __cinit__(self, value):
         self.value = value
+
+def test_exception_isinstance(maybe_exn):
+    """
+    >>> test_exception_isinstance(Exception())
+    True
+    >>> test_exception_isinstance(MyException(3))
+    True
+    >>> test_exception_isinstance(3)
+    False
+    """
+    return isinstance(maybe_exn, Exception)
+
+def test_exception_type_cast(Exception maybe_exn):
+    """
+    >>> test_exception_type_cast(Exception())
+    >>> test_exception_type_cast(MyException(3))
+    >>> test_exception_type_cast(3)   # doctest: +ELLIPSIS
+    Traceback (most recent call last):
+    ...
+    TypeError: Argument 'maybe_exn' has incorrect type (expected ...Exception, got int)
+    """
+    cdef object o = maybe_exn
+    cdef Exception e = o