:fix: possible recursion problems

Going through all members may be problematic when there is an infinite tree.
For example, float objects provide two data descriptor: real and imag.
Thus, you can have:

>>> f = 1.0
>>> f.imag.imag.imag.imag.imag.imag # ...

In this case, getfeatures just reaches the Maximum Depth Recursion.

To avoid this, getfeatures will only traverse through properties of type featuredprop.

doc/source/conf.py

@@ -60,9 +60,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '1.2'
+version = '2.0'
 # The full version, including alpha/beta/rc tags.
-release = '1.2'
+release = '2.0'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.

doc/source/tutorial.rst

@@ -43,15 +43,22 @@ You can now get a list of all features provided by an instance:
 
    # result == [(obj, JSONFeature)]
 
-**NB:** ``getfeatures()`` also look for instance members recursively:
+**NB:** ``getfeatures()`` look for featured properties (a special kind of
+property, used to indicate that there may be resolvable features):
 
 .. code-block:: python
 
+   from link.feature import featuredprop
+
    class Dummy(object):
        def __init__(self, *args, **kwargs):
            super(Dummy, self).__init__(*args, **kwargs)
 
-           self.inner = MyClass()
+           self._inner = MyClass()
+
+       @featuredprop
+       def inner(self):
+           return self._inner
 
    obj2 = Dummy()
    result = getfeatures(obj2)

link/feature/__init__.py

@@ -1,10 +1,14 @@
 # -*- coding: utf-8 -*-
 
-from link.feature.core import Feature
+from link.feature.core import Feature, featuredprop
 from link.feature.core import addfeatures, getfeatures
 from link.feature.core import hasfeature, getfeature
 
 
-__all__ = ['Feature', 'addfeatures', 'getfeatures', 'hasfeature', 'getfeature']
+__all__ = [
+    'Feature', 'featuredprop',
+    'addfeatures', 'getfeatures',
+    'hasfeature', 'getfeature'
+]
 
-__version__ = '1.2'
+__version__ = '2.0'

link/feature/core.py

@@ -19,6 +19,12 @@ def __init__(self, obj, *args, **kwargs):
         self.obj = obj
 
 
+class featuredprop(property):
+    """
+    Special property to allow traversal by the ``getfeatures()`` function.
+    """
+
+
 def addfeatures(features):
     """
     Add features to a class.
@@ -74,8 +80,8 @@ def _getfeatures(obj, cache):
 
             return result
 
-        if obj not in cache:
-            cache.add(obj)
+        if id(obj) not in cache:
+            cache.add(id(obj))
             bases = obj.__class__.mro()
 
             for base in reversed(bases):
@@ -84,16 +90,18 @@ def _getfeatures(obj, cache):
                     for feature_cls in getattr(base, '__features__', [])
                 ]
 
-            members = [
-                m
-                for n, m in getmembers(obj)
-                if not isroutine(m)
-                and not isclass(m)
-                and not n.startswith('__')
+            featuredpropnames = [
+                n
+                for n, m
+                in getmembers(
+                    obj.__class__,
+                    lambda m: isinstance(m, featuredprop)
+                )
             ]
 
-            for member in members:
-                result += _getfeatures(member, cache)
+            for propname in featuredpropnames:
+                attr = getattr(obj, propname)
+                result += _getfeatures(attr, cache)
 
         return result
 

link/feature/test/core.py

@@ -2,7 +2,7 @@
 
 from unittest import TestCase, main
 
-from link.feature.core import Feature
+from link.feature.core import Feature, featuredprop
 from link.feature.core import addfeatures, getfeatures
 from link.feature.core import hasfeature, getfeature
 
@@ -19,21 +19,25 @@ class TestFeature(TestCase):
     def setUp(self):
         # create circular reference for getfeatures tests
         def inner_init(this, dummy):
-            self.dummy = dummy
+            self._dummy = dummy
 
         self.inner_cls = type('InnerDummy', (object,), {
-            '__init__': inner_init
+            '__init__': inner_init,
+            'dummy': featuredprop(lambda s: s._dummy)
         })
 
         def dummy_init(this):
-            this.inner = self.inner_cls(this)
-            this.list_inner = [this.inner]
-            this.dict_inner = {
-                'key': this.inner
+            this._inner = self.inner_cls(this)
+            this._list_inner = [this._inner]
+            this._dict_inner = {
+                'key': this._inner
             }
 
         self.cls = type('Dummy', (object,), {
-            '__init__': dummy_init
+            '__init__': dummy_init,
+            'inner': featuredprop(lambda s: s._inner),
+            'list_inner': featuredprop(lambda s: s._list_inner),
+            'dict_inner': featuredprop(lambda s: s._dict_inner),
         })
 
     def test_addfeatures(self):