Scripted objects saving attributes
Introduction
Scripted objects are rebuilt every time a FCStd document is opened. To do this the document keeps a reference to the module and Python class that were used to create the object, along with its properties.
Attributes of the class used to create the object can also be saved, that is, "serialized". This can be further controlled by the __getstate__
and __setstate__
methods of the class.
Saving all attributes
By default, attributes saved in an object class are those from the __dict__
dictionary of the class.
# various_states.py
class VariousStates:
def __init__(self, obj):
obj.addProperty("App::PropertyLength", "Length")
obj.addProperty("App::PropertyArea", "Area")
obj.Length = 15
obj.Area = 300
obj.Proxy = self
Type = dict()
Type["Version"] = "Custom"
Type["Release"] = "production"
self.Type = Type
self.Type = "Custom"
self.ver = "0.18"
self.color = (0, 0, 1)
self.width = 2.5
def execute(self, obj):
pass
An object can be created using this class, and it can be saved to my_document.FCstd. If no particular viewprovider is assigned to the new object, its proxy class is simply set to a value different from None
, in this case, to 1
.
import FreeCAD as App
import various_states
doc = App.newDocument()
doc.FileName = "my_document.FCStd"
obj = doc.addObject("Part::FeaturePython", "Custom")
various_states.VariousStates(obj)
if App.GuiUp:
obj.ViewObject.Proxy = 1
doc.recompute()
doc.save()
When we re-open the file we can inspect the dictionary of the object's class.
>>> obj = App.ActiveDocument.Custom
>>> print(obj.Proxy)
<various_states.VariousStates object at 0x7f0a899bde10>
>>> print(obj.Proxy.__dict__)
{'Type': {'Version': 'Custom', 'Release': 'production'}, 'ver': '0.18', 'color': [0, 0, 1], 'width': 2.5}
We see that all attributes that start with self
in the class were saved. These can be of different types, including string, list, float, and dictionary. The original tuple for self.color
was converted to a list, but otherwise all attributes were loaded the same.
Saving specific attributes
We can define a class similar to the first one, that implements specific attributes to save.
# various_states.py
class CustomStates:
def __init__(self, obj):
obj.addProperty("App::PropertyLength", "Length")
obj.addProperty("App::PropertyArea", "Area")
obj.Length = 15
obj.Area = 300
obj.Proxy = self
Type = dict()
Type["Version"] = "Custom"
Type["Release"] = "production"
self.Type = Type
self.ver = "0.18"
self.color = (0, 0, 1)
self.width = 2.5
def execute(self, obj):
pass
def __getstate__(self):
return self.color, self.width
def __setstate__(self, state):
self.color = state[0]
self.width = state[1]
The return value of __getstate__
is the object that will be serialized. This can be a single value, or a tuple of values. When the object is restored, the class calls the __setstate__
method, passing the state
variable with the serialized content. In this case state
is a tuple that is unpacked into the respective variables to reconstruct the "state" that original existed.
state = (self.color, self.width)
state = ((0, 0, 1), 2.5)
We can create an object with this class, and save the document, just like in the previous example. When we re-open the file we can inspect the dictionary of the object's class.
>>> obj2 = App.ActiveDocument.Custom2
>>> print(obj2.Proxy)
<various_states.CustomStates object at 0x7fb399496630>
>>> print(obj2.Proxy.__dict__)
{'color': [0, 0, 1], 'width': 2.5}
The original tuple for self.color
was converted to a list, but otherwise the information was recovered fine. Instead of restoring all attributes like in the previous case, only the attributes that we specified in __getstate__
and __setstate__
were restored.
Links
- FreeCAD scripting: Python, Introduction to Python, Python scripting tutorial, FreeCAD Scripting Basics
- Modules: Builtin modules, Units, Quantity
- Workbenches: Workbench creation, Gui Commands, Commands, Installing more workbenches
- Meshes and Parts: Mesh Scripting, Topological data scripting, Mesh to Part, PythonOCC
- Parametric objects: Scripted objects, Viewproviders (Custom icon in tree view)
- Scenegraph: Coin (Inventor) scenegraph, Pivy
- Graphical interface: Interface creation, Interface creation completely in Python (1, 2, 3, 4, 5), PySide, PySide examples beginner, intermediate, advanced
- Macros: Macros, How to install macros
- Embedding: Embedding FreeCAD, Embedding FreeCADGui
- Other: Expressions, Code snippets, Line drawing function, FreeCAD vector math library (deprecated)
- Hubs: User hub, Power users hub, Developer hub