Fix FrozenClass attribute isolation and linting (#605)

* Initial plan

* Fix FrozenClass to use per-class attrs instead of shared

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

* Add missing return statement in __getattr__

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

* Add success message to test __main__ block

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

* Fix black formatting: remove trailing blank line

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

* Update pySDC/tests/test_helpers/test_frozen_class.py

Co-authored-by: Thomas Saupe <39156931+brownbaerchen@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>
Co-authored-by: Robert Speck <pancetta@users.noreply.github.com>
Co-authored-by: Thomas Saupe <39156931+brownbaerchen@users.noreply.github.com>

Author: 3 people

pySDC/helpers/pysdc_helper.py

@@ -9,10 +9,17 @@ class FrozenClass(object):
         __isfrozen: Flag to freeze a class
     """
 
-    attrs = []
-
     __isfrozen = False
 
+    def __init_subclass__(cls, **kwargs):
+        """
+        Called when a class inherits from FrozenClass.
+        Creates a separate attrs list for each subclass.
+        """
+        super().__init_subclass__(**kwargs)
+        # Create a new attrs list for this specific subclass
+        cls.attrs = []
+
     def __setattr__(self, key, value):
         """
         Function called when setting attributes
@@ -23,7 +30,7 @@ def __setattr__(self, key, value):
         """
 
         # check if attribute exists and if class is frozen
-        if self.__isfrozen and not (key in self.attrs or hasattr(self, key)):
+        if self.__isfrozen and not (key in type(self).attrs or hasattr(self, key)):
             raise TypeError(f'{type(self).__name__!r} is a frozen class, cannot add attribute {key!r}')
 
         object.__setattr__(self, key, value)
@@ -32,10 +39,10 @@ def __getattr__(self, key):
         """
         This is needed in case the variables have not been initialized after adding.
         """
-        if key in self.attrs:
+        if key in type(self).attrs:
             return None
         else:
-            super().__getattribute__(key)
+            return super().__getattribute__(key)
 
     @classmethod
     def add_attr(cls, key, raise_error_if_exists=False):
@@ -79,4 +86,4 @@ def __dir__(self):
         """
         My hope is that some editors can use this for dynamic autocompletion.
         """
-        return super().__dir__() + self.attrs
+        return super().__dir__() + type(self).attrs

pySDC/tests/test_helpers/test_frozen_class.py

@@ -29,8 +29,51 @@ class Dummy2(FrozenClass):
     Dummy2.add_attr('bar')
     you = Dummy2()
     you.bar = 5
-    assert me.bar is None, 'Attribute was set across classes'
+    # With the fix, 'bar' should NOT be accessible on Dummy instances at all
+    # because it was only added to Dummy2, not Dummy
+    with pytest.raises(AttributeError):  # bar is not an attribute of Dummy
+        _ = me.bar
+
+
+@pytest.mark.base
+def test_frozen_class_isolation():
+    """
+    Test that attributes added to one frozen class don't leak to other frozen classes.
+    This specifically tests the fix for the issue where attrs was shared across all subclasses.
+    """
+    from pySDC.helpers.pysdc_helper import FrozenClass
+
+    # Simulate Level and Step status classes from the issue
+    class LevelStatus(FrozenClass):
+        def __init__(self):
+            self.residual = None
+            self._freeze()
+
+    class StepStatus(FrozenClass):
+        def __init__(self):
+            self.iter = None
+            self._freeze()
+
+    # Add attribute to LevelStatus only
+    LevelStatus.add_attr('error_embedded_estimate')
+
+    # Verify attrs are separate
+    assert 'error_embedded_estimate' in LevelStatus.attrs
+    assert 'error_embedded_estimate' not in StepStatus.attrs
+
+    level_status = LevelStatus()
+    step_status = StepStatus()
+
+    # Should work - error_embedded_estimate was added to LevelStatus
+    level_status.error_embedded_estimate = 0.01
+    assert level_status.error_embedded_estimate == 0.01
+
+    # Should fail - error_embedded_estimate was NOT added to StepStatus
+    with pytest.raises(TypeError, match="is a frozen class, cannot add attribute"):
+        step_status.error_embedded_estimate = 0.02
 
 
 if __name__ == '__main__':
     test_frozen_class()
+    test_frozen_class_isolation()
+    print("All tests passed!")