simple possiblity for overriding properties

When a class attribute is assigned with the same name as a property
from an inherited class, the property default is overridden.
If the type does not match, a ProgrammingError is raised.

Change-Id: Ifdab5c8bbdaae008370a9b297c770f5c04db9311
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21989
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>

secop/properties.py

@@ -24,7 +24,7 @@
 
 from collections import OrderedDict
 
-from secop.errors import ProgrammingError, ConfigError
+from secop.errors import ProgrammingError, ConfigError, BadValueError
 
 
 # storage for 'properties of a property'
@@ -52,8 +52,9 @@ class Property:
         self.settable = settable or mandatory  # settable means settable from the cfg file
 
     def __repr__(self):
-        return 'Property(%r, %s, default=%r, extname=%r, export=%r, mandatory=%r)' % (
+        return 'Property(%r, %s, default=%r, extname=%r, export=%r, mandatory=%r, settable=%r)' % (
-            self.description, self.datatype, self.default, self.extname, self.export, self.mandatory)
+            self.description, self.datatype, self.default, self.extname, self.export,
+            self.mandatory, self.settable)
 
 
 class Properties(OrderedDict):
@@ -100,7 +101,8 @@ class PropertyMeta(type):
         for base in reversed(bases):
             properties.update(getattr(base, "properties", {}))
         # update with properties from new class
-        properties.update(attrs.get('properties', {}))
+        aprops = attrs.get('properties', {})
+        properties.update(aprops)
         newtype.properties = properties
 
         # generate getters
@@ -108,9 +110,23 @@ class PropertyMeta(type):
             def getter(self, pname=k):
                 val = self.__class__.properties[pname].default
                 return self.properties.get(pname, val)
-            if k in attrs:
+            if k in attrs and not isinstance(attrs[k], property):
-                if not isinstance(attrs[k], property):
+                if callable(attrs[k]):
-                    raise ProgrammingError('Name collision with property %r' % k)
+                    raise ProgrammingError('%r: property %r collides with method'
+                                        % (newtype, k))
+                if k in aprops:
+                    # this property was defined in the same class
+                    raise ProgrammingError('%r: name collision with property %r'
+                                        % (newtype, k))
+                # assume the attribute value should be assigned to the property
+                try:
+                    # make a copy first!
+                    prop = Property(**newtype.properties[k].__dict__)
+                    prop.default = prop.datatype(attrs[k])
+                    newtype.properties[k] = prop
+                except BadValueError:
+                    raise ProgrammingError('%r: property %r can not be set to %r'
+                                            % (newtype, k, attrs[k]))
             setattr(newtype, k, property(getter))
         return newtype
 

test/test_properties.py

@@ -114,6 +114,36 @@ def test_Property_checks():
     o.checkProperties()
     o = cl()
     o.checkProperties()
+    # test for min/max check
     o.setProperty('maxabc', 1)
     with pytest.raises(ConfigError):
         o.checkProperties()
+
+def test_Property_override():
+    o1 = c()
+    class co(c):
+        a = 3
+    o2 = co()
+    assert o1.a == 1
+    assert o2.a == 3
+
+    with pytest.raises(ProgrammingError) as e:
+        class cx(c): # pylint: disable=unused-variable
+            def a(self):
+                pass
+    assert 'collides with method' in str(e.value)
+
+    with pytest.raises(ProgrammingError) as e:
+        class cy(c): # pylint: disable=unused-variable
+            properties = {
+                'b' : Property('', FloatRange(), 3.14),
+            }
+            b = 1.5
+
+    assert 'name collision with property' in str(e.value)
+
+    with pytest.raises(ProgrammingError) as e:
+        class cz(c): # pylint: disable=unused-variable
+            a = 's'
+
+    assert 'can not be set to' in str(e.value)