Basic Operator Example

This script shows simple operator which prints a message.

Since the operator only has an Operator.execute function it takes no user input.


Operator subclasses must be registered before accessing them from blender.

import bpy

class HelloWorldOperator(bpy.types.Operator):
    bl_idname = "wm.hello_world"
    bl_label = "Minimal Operator"

    def execute(self, context):
        print("Hello World")
        return {'FINISHED'}


# test call to the newly defined operator

Invoke Function

Operator.invoke is used to initialize the operator from the context at the moment the operator is called. invoke() is typically used to assign properties which are then used by execute(). Some operators don’t have an execute() function, removing the ability to be repeated from a script or macro.

This example shows how to define an operator which gets mouse input to execute a function and that this operator can be invoked or executed from the python api.

Also notice this operator defines its own properties, these are different to typical class properties because blender registers them with the operator, to use as arguments when called, saved for operator undo/redo and automatically added into the user interface.

import bpy

class SimpleMouseOperator(bpy.types.Operator):
    """ This operator shows the mouse location,
        this string is used for the tooltip and API docs
    bl_idname = "wm.mouse_position"
    bl_label = "Invoke Mouse Operator"

    x = bpy.props.IntProperty()
    y = bpy.props.IntProperty()

    def execute(self, context):
        # rather than printing, use the report function,
        # this way the message appears in the header,
        self.report({'INFO'}, "Mouse coords are %d %d" % (self.x, self.y))
        return {'FINISHED'}

    def invoke(self, context, event):
        self.x = event.mouse_x
        self.y = event.mouse_y
        return self.execute(context)


# Test call to the newly defined operator.
# Here we call the operator and invoke it, meaning that the settings are taken
# from the mouse.

# Another test call, this time call execute() directly with pre-defined settings.
bpy.ops.wm.mouse_position('EXEC_DEFAULT', x=20, y=66)

Calling a File Selector

This example shows how an operator can use the file selector.

Notice the invoke function calls a window manager method and returns {'RUNNING_MODAL'}, this means the file selector stays open and the operator does not exit immediately after invoke finishes.

The file selector runs the operator, calling Operator.execute when the user confirms.

The Operator.poll function is optional, used to check if the operator can run.

import bpy

class ExportSomeData(bpy.types.Operator):
    """Test exporter which just writes hello world"""
    bl_idname = "export.some_data"
    bl_label = "Export Some Data"

    filepath = bpy.props.StringProperty(subtype="FILE_PATH")

    def poll(cls, context):
        return context.object is not None

    def execute(self, context):
        file = open(self.filepath, 'w')
        file.write("Hello World " + context.object.name)
        return {'FINISHED'}

    def invoke(self, context, event):
        return {'RUNNING_MODAL'}

# Only needed if you want to add into a dynamic menu
def menu_func(self, context):
    self.layout.operator_context = 'INVOKE_DEFAULT'
    self.layout.operator(ExportSomeData.bl_idname, text="Text Export Operator")

# Register and add to the file selector

# test call

Dialog Box

This operator uses its Operator.invoke function to call a popup.

import bpy

class DialogOperator(bpy.types.Operator):
    bl_idname = "object.dialog_operator"
    bl_label = "Simple Dialog Operator"

    my_float = bpy.props.FloatProperty(name="Some Floating Point")
    my_bool = bpy.props.BoolProperty(name="Toggle Option")
    my_string = bpy.props.StringProperty(name="String Value")

    def execute(self, context):
        message = "Popup Values: %f, %d, '%s'" % \
            (self.my_float, self.my_bool, self.my_string)
        self.report({'INFO'}, message)
        return {'FINISHED'}

    def invoke(self, context, event):
        wm = context.window_manager
        return wm.invoke_props_dialog(self)


# test call

Custom Drawing

By default operator properties use an automatic user interface layout. If you need more control you can create your own layout with a Operator.draw function.

This works like the Panel and Menu draw functions, its used for dialogs and file selectors.

import bpy

class CustomDrawOperator(bpy.types.Operator):
    bl_idname = "object.custom_draw"
    bl_label = "Simple Modal Operator"

    filepath = bpy.props.StringProperty(subtype="FILE_PATH")

    my_float = bpy.props.FloatProperty(name="Float")
    my_bool = bpy.props.BoolProperty(name="Toggle Option")
    my_string = bpy.props.StringProperty(name="String Value")

    def execute(self, context):
        print("Test", self)
        return {'FINISHED'}

    def invoke(self, context, event):
        wm = context.window_manager
        return wm.invoke_props_dialog(self)

    def draw(self, context):
        layout = self.layout
        col = layout.column()
        col.label(text="Custom Interface!")

        row = col.row()
        row.prop(self, "my_float")
        row.prop(self, "my_bool")

        col.prop(self, "my_string")


# test call