Draft: clean up the internal DraftAnnotation class

Add a function to clarify the added properties,
and clean up the PEP8 style of the code.

src/Mod/Draft/draftobjects/draft_annotation.py

@@ -1,5 +1,6 @@
 # ***************************************************************************
-# *   (c) 2020 Carlo Pavan                                                  *
+# *   Copyright (c) 2020 Carlo Pavan <carlopav@gmail.com>                   *
+# *   Copyright (c) 2020 Eliud Cabrera Castillo <e.cabrera-castillo@tum.de> *
 # *                                                                         *
 # *   This file is part of the FreeCAD CAx development system.              *
 # *                                                                         *
@@ -20,11 +21,19 @@
 # *   USA                                                                   *
 # *                                                                         *
 # ***************************************************************************
-"""This module provides the object code for Draft Annotation.
+"""Provide the basic object code for all Draft annotation objects.
+
+This is used by many objects that show dimensions and text created on screen
+through Coin (pivy).
+- DimensionBase
+- LinearDimension
+- AngularDimension
+- Label
+- Text
 """
-## @package annotation
+## @package draft_annotation
 # \ingroup DRAFT
-# \brief This module provides the object code for Draft Annotation.
+# \brief Provide the basic object code for all Draft annotation objects.
 
 from PySide.QtCore import QT_TRANSLATE_NOOP
 
@@ -44,41 +53,62 @@ class DraftAnnotation(object):
     Text
     """
 
-    def __init__(self, obj, tp="Annotation"):
-        self.Type = tp
+    def __init__(self, obj, typ="Annotation"):
+        self.Type = typ
+        obj.Proxy = self
 
     def onDocumentRestored(self, obj):
-        """Run when the document that is using this class is restored.
+        """Execute code when the document is restored.
 
         Check if new properties are present after the object is restored
         in order to migrate older objects.
         """
-        if hasattr(obj, "ViewObject") and obj.ViewObject:
-            if not hasattr(obj.ViewObject, 'ScaleMultiplier'):
-                # annotation properties
-                vobj = obj.ViewObject
-                _tip = QT_TRANSLATE_NOOP("App::Property",
-                        "Dimension size overall multiplier")
-                vobj.addProperty("App::PropertyFloat", "ScaleMultiplier", "Annotation", _tip)
-                vobj.ScaleMultiplier = 1.00
-
-                _info = "added view property 'ScaleMultiplier'"
-                _wrn("v0.19, " + obj.Label + ", " + _tr(_info))
+        self.add_missing_properties_0v19(obj)
+
+    def add_missing_properties_0v19(self, obj):
+        """Provide missing annotation properties, if they don't exist."""
+        if (hasattr(obj, "ViewObject") and obj.ViewObject
+                and not hasattr(obj.ViewObject, 'ScaleMultiplier')):
+            vobj = obj.ViewObject
+            _tip = QT_TRANSLATE_NOOP("App::Property",
+                                     "Dimension size overall multiplier")
+            vobj.addProperty("App::PropertyFloat",
+                             "ScaleMultiplier",
+                             "Annotation",
+                             _tip)
+            vobj.ScaleMultiplier = 1.00
+
+            _info = "added view property 'ScaleMultiplier'"
+            _wrn("v0.19, " + obj.Label + ", " + _tr(_info))
 
     def __getstate__(self):
+        """Return a tuple of objects to save or None.
+
+        Save the Type.
+        """
         return self.Type
 
     def __setstate__(self, state):
+        """Set the internal properties from the restored state.
+
+        Restore the Type of the object.
+        """
         if state:
             if isinstance(state, dict) and ("Type" in state):
                 self.Type = state["Type"]
             else:
                 self.Type = state
 
     def execute(self, obj):
-        """Do something when recompute object."""
+        """Execute when the object is created or recomputed.
+
+        Does nothing.
+        """
         return
 
     def onChanged(self, obj, prop):
-        """Do something when a property has changed."""
+        """Execute when a property is changed.
+
+        Does nothing.
+        """
         return