Merge pull request #214 from weka-io/better-aliasing-exceptions

Improve `RecursionError` for aliasing-induced infinite recursion

Author: idanarye

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - units: DataSize - return 'byte' and 'MiB' instead of '1 byte' and '1 MiB'
 - units: Duration(inf) is now 'Eternity' instead of 'Never'
 - timing: The Timer class now renders the duration using the Duration's repr, instead of as a float
+- aliasing: Improved `RecursionError` for aliasing-induced infinite recursion
 
 ### Added
 - CLI: expose 'colorize' and 'ziplog' as clis

easypy/aliasing.py

@@ -13,6 +13,13 @@ def super_dir(obj):
     return sorted(set(chain(dir(type(obj)), obj.__dict__)))
 
 
+# Python 3.4 does not have RecursionError - it throws a RuntimeError instead
+try:
+    _RecursionError = RecursionError
+except NameError:
+    _RecursionError = RuntimeError
+
+
 class AliasingMixin():
     @property
     def _aliased(self):
@@ -29,7 +36,16 @@ def __dir__(self):
     def __getattr__(self, attr):
         if attr.startswith("_"):
             raise AttributeError(attr)
-        return getattr(self._aliased, attr)
+        try:
+            return getattr(self._aliased, attr)
+        except _RecursionError as e:
+            if type(e) is RuntimeError and str(e) != 'maximum recursion depth exceeded':
+                raise
+            raise _RecursionError('Infinite recursion trying to access {attr!r} on {obj!r} (via {type_name}.{alias}.{attr})'.format(
+                attr=attr,
+                obj=self,
+                type_name=type(self).__name__,
+                alias=self._ALIAS))
 
 
 def aliases(name, static=True):

tests/test_aliasing.py

@@ -41,3 +41,24 @@ def __init__(self, x):
     f = Foo("5")
     assert f.get("a") == 1
     assert f == 5
+
+
+def test_aliasing_infinite_recursion_exception():
+    @aliases('bar', static=False)
+    class Foo:
+        def __init__(self):
+            self.bar = Bar(self)
+
+        def __repr__(self):
+            return 'Foo()'
+
+    class Bar:
+        def __init__(self, foo):
+            self.foo = foo
+
+        def baz(self):
+            return self.foo.baz()
+
+    with pytest.raises(getattr(__builtins__, 'RecursionError', RuntimeError)) as e:
+        Foo().baz()
+    assert str(e.value) == "Infinite recursion trying to access 'baz' on Foo() (via Foo.bar.baz)"