Quickstart Introduction


This API is generally stable but some areas are still being added and improved.

The Blender/Python API can do the following:

  • Edit any data the user interface can (Scenes, Meshes, Particles etc.)
  • Modify user preferences, keymaps and themes
  • Run tools with own settings
  • Create user interface elements such as menus, headers and panels
  • Create new tools
  • Create interactive tools
  • Create new rendering engines that integrate with Blender
  • Define new settings in existing Blender data
  • Draw in the 3D view using OpenGL commands from Python

The Blender/Python API can’t (yet)...

  • Create new space types.
  • Assign custom properties to every type.
  • Define callbacks or listeners to be notified when data is changed.

Before Starting

This document isn’t intended to fully cover each topic. Rather, its purpose is to familiarize you with Blender 2.5’s new Python API.

A quick list of helpful things to know before starting:

  • Blender uses Python 3.x; some 3rd party extensions are not available yet.
  • The interactive console in Blender 2.5 has been improved; testing one-liners in the console is a good way to learn.
  • Button tool tips show Python attributes and operator names.
  • Right clicking on buttons and menu items directly links to API documentation.
  • For more examples, the text menu has a templates section where some example operators can be found.
  • To examine further scripts distributed with Blender, see ~/.blender/scripts/startup/bl_ui for the user interface and ~/.blender/scripts/startup/bl_op for operators.

Key Concepts

Data Access

Accessing datablocks

Python accesses Blender’s data in the same way as the animation system and user interface; this implies that any setting that can be changed via a button can also be changed from Python.

Accessing data from the currently loaded blend file is done with the module bpy.data. This gives access to library data. For example:

>>> bpy.data.objects
<bpy_collection[3], BlendDataObjects>
>>> bpy.data.scenes
<bpy_collection[1], BlendDataScenes>
>>> bpy.data.materials
<bpy_collection[1], BlendDataMaterials>

About Collections

You’ll notice that an index as well as a string can be used to access members of the collection.

Unlike Python’s dictionaries, both methods are acceptable; however, the index of a member may change while running Blender.

>>> list(bpy.data.objects)
[bpy.data.objects["Cube"], bpy.data.objects["Plane"]]
>>> bpy.data.objects['Cube']
>>> bpy.data.objects[0]

Accessing attributes

Once you have a data block, such as a material, object, groups etc., its attributes can be accessed much like you would change a setting using the graphical interface. In fact, the tooltip for each button also displays the Python attribute which can help in finding what settings to change in a script.

>>> bpy.data.objects[0].name
>>> bpy.data.scenes["Scene"]
>>> bpy.data.materials.new("MyMaterial")

For testing what data to access it’s useful to use the “Console”, which is its own space type in Blender 2.5. This supports auto-complete, giving you a fast way to dig into different data in your file.

Example of a data path that can be quickly found via the console:

>>> bpy.data.scenes[0].render.resolution_percentage
>>> bpy.data.scenes[0].objects["Torus"].data.vertices[0].co.x

Custom Properties

Python can access properties on any datablock that has an ID (data that can be linked in and accessed from bpy.data. When assigning a property, you can make up your own names, these will be created when needed or overwritten if they exist.

This data is saved with the blend file and copied with objects.


bpy.context.object["MyOwnProperty"] = 42

if "SomeProp" in bpy.context.object:
    print("Property found")

# Use the get function like a python dictionary
# which can have a fallback value.
value = bpy.data.scenes["Scene"].get("test_prop", "fallback value")

# dictionaries can be assigned as long as they only use basic types.
group = bpy.data.groups.new("MyTestGroup")
group["GameSettings"] = {"foo": 10, "bar": "spam", "baz": {}}

del group["GameSettings"]

Note that these properties can only be assigned basic Python types.

  • int, float, string
  • array of ints/floats
  • dictionary (only string keys are supported, values must be basic types too)

These properties are valid outside of Python. They can be animated by curves or used in driver paths.


While it’s useful to be able to access data directly by name or as a list, it’s more common to operate on the user’s selection. The context is always available from ‘’‘bpy.context’‘’ and can be used to get the active object, scene, tool settings along with many other attributes.

Common-use cases:

>>> bpy.context.object
>>> bpy.context.selected_objects
>>> bpy.context.visible_bones

Note that the context is read-only. These values cannot be modified directly, though they may be changed by running API functions or by using the data API.

So bpy.context.object = obj will raise an error.

But bpy.context.scene.objects.active = obj will work as expected.

The context attributes change depending on where they are accessed. The 3D view has different context members than the console, so take care when accessing context attributes that the user state is known.

See bpy.context API reference

Operators (Tools)

Operators are tools generally accessed by the user from buttons, menu items or key shortcuts. From the user perspective they are a tool but Python can run these with its own settings through the bpy.ops module.


>>> bpy.ops.mesh.flip_normals()
>>> bpy.ops.mesh.hide(unselected=False)
>>> bpy.ops.object.scale_apply()


The menu item: Help -> Operator Cheat Sheet” gives a list of all operators and their default values in Python syntax, along with the generated docs. This is a good way to get an overview of all blender’s operators.

Operator Poll()

Many operators have a “poll” function which may check that the mouse is a valid area or that the object is in the correct mode (Edit Mode, Weight Paint etc). When an operator’s poll function fails within python, an exception is raised.

For example, calling bpy.ops.view3d.render_border() from the console raises the following error:

RuntimeError: Operator bpy.ops.view3d.render_border.poll() failed, context is incorrect

In this case the context must be the 3d view with an active camera.

To avoid using try/except clauses wherever operators are called you can call the operators own .poll() function to check if it can run in the current context.

if bpy.ops.view3d.render_border.poll():


Python scripts can integrate with Blender in the following ways:

  • By defining a rendering engine.
  • By defining operators.
  • By defining menus, headers and panels.
  • By inserting new buttons into existing menus, headers and panels

In Python, this is done by defining a class, which is a subclass of an existing type.

Example Operator

import bpy

def main(context):
    for ob in context.scene.objects:

class SimpleOperator(bpy.types.Operator):
    bl_idname = "object.simple_operator"
    bl_label = "Simple Object Operator"

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

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

def register():

def unregister():

if __name__ == "__main__":

    # test call

Once this script runs, SimpleOperator is registered with Blender and can be called from the operator search popup or added to the toolbar.

To run the script:

  1. Highlight the above code then press Ctrl+C to copy it.
  2. Start Blender
  3. Press Ctrl+Right twice to change to the Scripting layout.
  4. Click the button labeled New and the confirmation pop up in order to create a new text block.
  5. Press Ctrl+V to paste the code into the text panel (the upper left frame).
  6. Click on the button Run Script.
  7. Move you’re mouse into the 3D view, press spacebar for the operator search menu, and type “Simple”.
  8. Click on the “Simple Operator” item found in search.

See also

The class members with the bl_ prefix are documented in the API reference bpy.types.Operator


The output from the main function is sent to the terminal; in order to see this, be sure to use the terminal.

Example Panel

Panels register themselves as a class, like an operator. Notice the extra bl_ variables used to set the context they display in.

import bpy

class HelloWorldPanel(bpy.types.Panel):
    bl_label = "Hello World Panel"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = "PROPERTIES"
    bl_region_type = "WINDOW"
    bl_context = "object"

    def draw(self, context):
        layout = self.layout

        obj = context.object

        row = layout.row()
        row.label(text="Hello world!", icon='WORLD_DATA')

        row = layout.row()
        row.label(text="Active object is: " + obj.name)
        row = layout.row()
        row.prop(obj, "name")

def register():

def unregister():

if __name__ == "__main__":

To run the script:

  1. Highlight the above code then press Ctrl+C to copy it
  2. Start Blender
  3. Press Ctrl+Right twice to change to the Scripting layout
  4. Click the button labeled New and the confirmation pop up in order to create a new text block.
  5. Press Ctrl+V to paste the code into the text panel (the upper left frame)
  6. Click on the button Run Script.

To view the results:

  1. Select the the default cube.
  2. Click on the Object properties icon in the buttons panel (far right; appears as a tiny cube).
  3. Scroll down to see a panel named Hello World Panel.
  4. Changing the object name also updates Hello World Panel’s Name: field.

Note the row distribution and the label and properties that are available through the code.

See also



Blender defines a number of Python types but also uses Python native types.

Blender’s Python API can be split up into 3 categories.

Native Types

In simple cases returning a number or a string as a custom type would be cumbersome, so these are accessed as normal python types.

  • blender float/int/boolean -> float/int/boolean

  • blender enumerator -> string

    >>> C.object.rotation_mode = 'AXIS_ANGLE'
  • blender enumerator (multiple) -> set of strings

    # setting multiple camera overlay guides
    bpy.context.scene.camera.data.show_guide = {'GOLDEN', 'CENTER'}
    # passing as an operator argument for report types
    self.report({'WARNING', 'INFO'}, "Some message!")

Internal Types

Used for Blender datablocks and collections: bpy.types.bpy_struct

For data that contains its own attributes groups/meshes/bones/scenes... etc.

There are 2 main types that wrap Blenders data, one for datablocks (known internally as bpy_struct), another for properties.

>>> bpy.context.object
>>> C.scene.objects

Note that these types reference Blender’s data so modifying them is immediately visible.

Mathutils Types

Used for vectors, quaternion, eulers, matrix and color types, accessible from mathutils

Some attributes such as bpy.types.Object.location, bpy.types.PoseBone.rotation_euler and bpy.types.Scene.cursor_location can be accessed as special math types which can be used together and manipulated in various useful ways.

Example of a matrix, vector multiplication:

bpy.context.object.matrix_world * bpy.context.object.data.verts[0].co


mathutils types keep a reference to Blender’s internal data so changes can be applied back.


# modifies the Z axis in place.
bpy.context.object.location.z += 2.0

# location variable holds a reference to the object too.
location = bpy.context.object.location
location *= 2.0

# Copying the value drops the reference so the value can be passed to
# functions and modified without unwanted side effects.
location = bpy.context.object.location.copy()


There are 2 ways to add keyframes through Python.

The first is through key properties directly, which is similar to inserting a keyframe from the button as a user. You can also manually create the curves and keyframe data, then set the path to the property. Here are examples of both methods.

Both examples insert a keyframe on the active object’s Z axis.

Simple example:

obj = bpy.context.object
obj.location[2] = 0.0
obj.keyframe_insert(data_path="location", frame=10.0, index=2)
obj.location[2] = 1.0
obj.keyframe_insert(data_path="location", frame=20.0, index=2)

Using Low-Level Functions:

obj = bpy.context.object
obj.animation_data.action = bpy.data.actions.new(name="MyAction")
fcu_z = obj.animation_data.action.fcurves.new(data_path="location", index=2)
fcu_z.keyframe_points[0].co = 10.0, 0.0
fcu_z.keyframe_points[1].co = 20.0, 1.0