How to share variable among more than 2 operation

Question

I have a question about blender's python script. I would like to share variables among more than two operations, however I don't know how to.

If I use global variable, it's easy to solve this problem.

selected_faces = []
class SelectFace(bpy.types.Operator):
    bl_label = "Select Face"
    def execute(self, context):
        global selected_faces
        selected_faces = ...   # get selected faces.
        .....
class OperationAboutSelectedFaces(bpy.types.Operator):
    bl_label = "Operation About selected Face"
    def execute(self, context):
        global selected_faces
        # some operation to "selected_faces"

However, I want to avoid using global variable. So, I would like to rewrite this code as follows...

class SelectFace(bpy.types.Operator):
    bl_label = "Select Face"
    def execute(self, context):
        selected_faces = ... # get selected faces.
        .....
class OperationAboutSelectedFaces(bpy.types.Operator):
    bl_label = "Operation About selected Face"
    def execute(self, context):
        # some operation to "selected_faces"

Assuming operation sequence are as follows.

1. "Select Face"
2. "Operation About selected faces"

Thanks!

Answer 1

Finally, I solved this problem using static variable.

class SelectFace(bpy.types.Operator):
    bl_label = "Select Face"
    selected_faces = None
    def __init__(self):
        SelectFace.selected_faces = None
    def execute(self, context):
        SelectFace.selected_faces = ... # get selected faces.
        .....
class OperationAboutSelectedFaces(bpy.types.Operator):
    bl_label = "Operation About selected Face"
    def __init__(self):
        selected_faces = SelectFace.selected_faces
    def execute(self, context):
        # some operation to "selected_faces"

Thanks for your advice.

Answer 2

I could solve this problem.

Solution is shown below.

• Create user defined class which has properties you want.
• Register class to bpy.types.Scene.XXXXX when add-on is started
• Get data from bpy.context.scene.XXXXX
• Unregister class to bpy.types.Scene.XXXXX when add-on is stopped

class SelectFaceProp():
    selected_faces = None

class SelectFace(bpy.types.Operator):
    bl_label = "Select Face"
    def execute(self, context):
        props = bpy.context.scene.sf_props
        props.selected_faces = ... # get selected faces.
        .....
class OperationAboutSelectedFaces(bpy.types.Operator):
    bl_label = "Operation About selected Face"
    def execute(self, context):
        props = bpy.context.scene.sf_props
        # some operation to "props.selected_faces"

def register():
    bpy.types.Scene.sf_props = SelectFaceProp()

def unregister():
    del bpy.types.Scene.sf_props

Thank you!!!

Answer 3

You should not use global or static variables, the proper concept to use is Blender's context. Note that this is not a Python mechanism, but something provided by Blender.

The context keeps track of the state of Blender in things such as 'what is the selected scene? what is the active object? what is the current selection?'. This information can then be used by all of Blender's operators, not just your own. Operators, in turn, also affect the context, by for example, modifying the current selection. If you bypass the context, there will be some inconsistencies, such as operators working on your previous selection, because you never changed it in the context.

How to set that a given face is selected:

face.selected = True

Hot to get all selected faces in a mesh:

selected_faces = [face for face in mesh.faces if face.select]

The mesh can be obtained from the context that is passed as an argument to the operator's execute.