Operators (bpy.ops)

Calling Operators

Provides python access to calling operators, this includes operators written in C, Python or macros.

Only keyword arguments can be used to pass operator properties.

Operators don’t have return values as you might expect, instead they return a set() which is made up of: {'RUNNING_MODAL', 'CANCELLED', 'FINISHED', 'PASS_THROUGH'}. Common return values are {'FINISHED'} and {'CANCELLED'}.

Calling an operator in the wrong context will raise a RuntimeError, there is a poll() method to avoid this problem.

Note that the operator ID (bl_idname) in this example is mesh.subdivide, bpy.ops is just the access path for python.

Keywords and Positional Arguments

For calling operators keywords are used for operator properties and positional arguments are used to define how the operator is called.

There are 3 optional positional arguments (documented in detail below).

bpy.ops.test.operator(override_context, execution_context, undo)
  • override_context - dict type.
  • execution_context - str (enum).
  • undo - bool type.

Each of these arguments is optional, but must be given in the order above.

import bpy

# calling an operator
bpy.ops.mesh.subdivide(number_cuts=3, smoothness=0.5)


# check poll() to avoid exception.
if bpy.ops.object.mode_set.poll():
    bpy.ops.object.mode_set(mode='EDIT')

Overriding Context

It is possible to override context members that the operator sees, so that they act on specified rather than the selected or active data, or to execute an operator in the different part of the user interface.

The context overrides are passed as a dictionary, with keys matching the context member names in bpy.context. For example to override bpy.context.active_object, you would pass {'active_object': object}.

Note

You will nearly always want to use a copy of the actual current context as basis (otherwise, you’ll have to find and gather all needed data yourself).


# remove all objects in scene rather than the selected ones
import bpy
override = bpy.context.copy()
override['selected_bases'] = list(bpy.context.scene.object_bases)
bpy.ops.object.delete(override)

Execution Context

When calling an operator you may want to pass the execution context.

This determines the context that is given for the operator to run in, and whether invoke() is called or only execute().

‘EXEC_DEFAULT’ is used by default, running only the execute() method, but you may want the operator to take user interaction with ‘INVOKE_DEFAULT’ which will also call invoke() if existing.

The execution context is one of: (‘INVOKE_DEFAULT’, ‘INVOKE_REGION_WIN’, ‘INVOKE_REGION_CHANNELS’, ‘INVOKE_REGION_PREVIEW’, ‘INVOKE_AREA’, ‘INVOKE_SCREEN’, ‘EXEC_DEFAULT’, ‘EXEC_REGION_WIN’, ‘EXEC_REGION_CHANNELS’, ‘EXEC_REGION_PREVIEW’, ‘EXEC_AREA’, ‘EXEC_SCREEN’)


# group add popup
import bpy
bpy.ops.object.group_instance_add('INVOKE_DEFAULT')

It is also possible to run an operator in a particular part of the user interface. For this we need to pass the window, screen, area and sometimes a region.


# maximize 3d view in all windows
import bpy

for window in bpy.context.window_manager.windows:
    screen = window.screen

    for area in screen.areas:
        if area.type == 'VIEW_3D':
            override = {'window': window, 'screen': screen, 'area': area}
            bpy.ops.screen.screen_full_area(override)
            break