FrozenClass performance fix (#452)

* Fix for `FrozenClass` where attributes could be added multiple times.

* Didn't find a nice quick fix for attributes being added to all classes

* Fixed test

pySDC/helpers/pysdc_helper.py

@@ -1,3 +1,6 @@
+import logging
+
+
 class FrozenClass(object):
     """
     Helper class to freeze a class, i.e. to avoid adding more attributes
@@ -43,9 +46,15 @@ def add_attr(cls, key, raise_error_if_exists=False):
             key (str): The key to add
             raise_error_if_exists (bool): Raise an error if the attribute already exists in the class
         """
-        if key in cls.attrs and raise_error_if_exists:
-            raise TypeError(f'Attribute {key!r} already exists in {cls.__name__}!')
-        cls.attrs += [key]
+        logger = logging.getLogger(cls.__name__)
+        if key in cls.attrs:
+            if raise_error_if_exists:
+                raise TypeError(f'Attribute {key!r} already exists in {cls.__name__}!')
+            else:
+                logger.debug(f'Skip adding attribute {key!r} because it already exists in {cls.__name__}!')
+        else:
+            cls.attrs += [key]
+            logger.debug(f'Added attribute {key!r} to {cls.__name__}')
 
     def _freeze(self):
         """

pySDC/tests/test_helpers/test_frozen_class.py

@@ -0,0 +1,36 @@
+import pytest
+
+
+@pytest.mark.base
+def test_frozen_class():
+    from pySDC.helpers.pysdc_helper import FrozenClass
+
+    class Dummy(FrozenClass):
+        pass
+
+    me = Dummy()
+    me.add_attr('foo')
+
+    me.foo = 0
+
+    you = Dummy()
+    you.foo = 1
+    assert me.foo != you.foo, 'Attribute is shared between class instances'
+
+    me = Dummy()
+    assert me.foo is None, 'Attribute persists after reinstantiation'
+
+    me.add_attr('foo')
+    assert Dummy.attrs.count('foo') == 1, 'Attribute was added too many times'
+
+    class Dummy2(FrozenClass):
+        pass
+
+    Dummy2.add_attr('bar')
+    you = Dummy2()
+    you.bar = 5
+    assert me.bar is None, 'Attribute was set across classes'
+
+
+if __name__ == '__main__':
+    test_frozen_class()