Merge pull request #53 from lubieowoce/fix-getattr

Fixed infinite recursion when pytypes tries to access  .__orig_class__ on an instance of a @TypeChecked class with __getattr__/__getattribute__

Author: Stewori

pytypes/type_util.py

@@ -162,9 +162,26 @@ def _extra(tp):
     return None
 
 
+def _get_orig_class(obj):
+    """Returns  `obj.__orig_class__` protecting from infinite recursion in `__getattr[ibute]__` wrapped in a `checker_tp`.
+    (See `checker_tp` in `typechecker._typeinspect_func for context)
+    Necessary if:
+    - we're wrapping a method (`obj` is `self`/`cls`) and either
+        - the object's class defines __getattribute__
+    or
+        - the object doesn't have an `__orig_class__` attribute
+          and the object's class defines __getattr__.
+    In such a situation, `parent_class = obj.__orig_class__`
+    would call `__getattr[ibute]__`. But that method is wrapped in a `checker_tp` too,
+    so then we'd go into the wrapped `__getattr[ibute]__` and do
+    `parent_class = obj.__orig_class__`, which would call `__getattr[ibute]__` again, and so on.
+    So to bypass `__getattr[ibute]__` we do this: """
+    return object.__getattribute__(obj, '__orig_class__')
+
+
 def get_Generic_type(ob):
     try:
-        return ob.__orig_class__
+        return _get_orig_class(ob)
     except AttributeError:
         return ob.__class__
 
@@ -499,7 +516,7 @@ def _deep_type(obj, checked, checked_len, depth = None, max_sample = None, get_t
     if get_type is None:
         get_type = type
     try:
-        res = obj.__orig_class__
+        res = _get_orig_class(obj)
     except AttributeError:
         res = get_type(obj)
     if depth == 0 or util._is_in(obj, checked[:checked_len]):

pytypes/typechecker.py

@@ -33,7 +33,7 @@
 from .type_util import type_str, has_type_hints, _has_type_hints, is_builtin_type, \
         deep_type, _funcsigtypes, _issubclass, _isinstance, _find_typed_base_method, \
         _preprocess_typecheck, _raise_typecheck_error, _check_caller_type, TypeAgent, \
-        _check_as_func, is_Tuple
+        _check_as_func, is_Tuple, _get_orig_class
 from . import util, type_util
 
 try:
@@ -797,7 +797,7 @@ def checker_tp(*args, **kw):
         parent_class = None
         if slf:
             try:
-                parent_class = args_kw[0].__orig_class__
+                parent_class = _get_orig_class(args_kw[0])
             except AttributeError:
                 parent_class = args_kw[0].__class__
         elif clsm:

tests/test_typechecker.py

@@ -1372,6 +1372,38 @@ def meth_2(self, c):
         return 3*len(c)
 
 
+@typechecked
+class GetAttrDictWrapper(object):
+    """Test a plausible use of __getattr__ -
+    A class that wraps a dict, enabling the values to be accessed as if they were attributes
+    (`d.abc` instead of `d['abc']`)
+    For example, the `pyrsistent` library does this on its dict replacement.
+
+    >>> o = GetAttrDictWrapper({'a': 5, 'b': 10})
+    >>> o.a
+    5
+    >>> o.b
+    10
+    >>> o.nonexistent
+    Traceback (most recent call last):
+      ...
+    AttributeError('nonexistent')
+    
+    """
+
+    def __init__(self, dct):
+        # type: (dict) -> None
+        self.__dct = dct
+
+    def __getattr__(self, attr):
+        # type: (str) -> typing.Any
+        dct = self.__dct # can safely access the attribute because it exists so it won't trigger __getattr__
+        try:
+            return dct[attr]
+        except KeyError:
+            raise AttributeError(attr)
+
+
 class TestTypecheck(unittest.TestCase):
     def test_function(self):
         self.assertEqual(testfunc(3, 2.5, 'abcd'), (9, 7.5))
@@ -2560,6 +2592,23 @@ def test_staticmethod(self):
                 tc.testmeth_static2(11, ('a', 'b'), 1.9))
 
 
+class TestTypecheck_class_with_getattr(unittest.TestCase):
+    """
+    See pull request:
+    https://github.com/Stewori/pytypes/pull/53
+    commit #:
+    e2523b347e52707f87d7078daad1a93940c12e2e
+    """
+    def test_valid_access(self):
+        obj = GetAttrDictWrapper({'a': 5, 'b': 10})
+        self.assertEqual(obj.a, 5)
+        self.assertEqual(obj.b, 10)
+
+    def test_invalid_access(self):
+        obj = GetAttrDictWrapper({'a': 5, 'b': 10})
+        self.assertRaises(AttributeError, lambda: obj.nonexistent)
+
+
 class TestTypecheck_module(unittest.TestCase):
     def test_function_py2(self):
         from testhelpers import modulewide_typecheck_testhelper_py2 as mth