Blender as a Python Module

Blender supports being built as a Python module, allowing import bpy to be added to any Python script, providing access to Blender’s features.

Note

At time of writing official builds are not available, using this requires compiling Blender yourself see build instructions.

Use Cases

Python developers may wish to integrate Blender scripts which don’t center around Blender.

Possible uses include:

  • Visualizing data by rendering images and animations.

  • Image processing using Blender’s compositor.

  • Video editing (using Blender’s sequencer).

  • 3D file conversion.

  • Development, accessing bpy from Python IDE’s and debugging tools for example.

  • Automation.

Usage

For the most part using Blender as a Python module is equivalent to running a script in background-mode (passing the command-line arguments --background or -b), however there are some differences to be aware of.

Blender’s Executable Access

The attribute bpy.app.binary_path defaults to an empty string.

If you wish to point this to the location of a known executable you may set the value.

This example searches for the binary, setting it when found:

import bpy
import shutil

blender_bin = shutil.which("blender")
if blender_bin:
   print("Found:", blender_bin)
   bpy.app.binary_path = blender_bin
else:
   print("Unable to find blender!")
Blender’s Internal Modules

There are many modules included with Blender such as gpu and mathuils. It’s important that these are imported after bpy or they will not be found.

Command Line Arguments Unsupported

Functionality controlled by command line arguments (shown by calling blender --help aren’t accessible).

Typically this isn’t such a limitation although there are some command line arguments that don’t have equivalents in Blender’s Python API (--threads and --log for example).

Note

Access to these settings may be added in the future as needed.

Resource Sharing (GPU)

It’s possible other Python modules make use of the GPU in a way that prevents Blender/Cycles from accessing the GPU.

Signal Handlers

Blender’s typical signal handlers are not initialized, so there is no special handling for Control-C to cancel a render and a crash log is not written in the event of a crash.

Startup and Preferences

When the bpy module loads it contains the default startup scene (instead of an “empty” blend-file as you might expect), so there is a default cube, camera and light.

If you wish to start from an empty file use: bpy.ops.wm.read_factory_settings(use_empty=True).

The users startup and preferences are ignored to prevent your local configuration from impacting scripts behavior. The Python module behaves as if --factory-startup was passed as a command line argument.

The users preferences and startup can be loaded using operators:

import bpy

bpy.ops.wm.read_userpref()
bpy.ops.wm.read_homefile()

Limitations

Most constraints of Blender as an application still apply:

Reloading Unsupported

Reloading the bpy module via importlib.reload will raise an exception instead of reloading and resetting the module.

Instead, the operator bpy.ops.wm.read_factory_settings() can be used to reset the internal state.

Single Blend File Restriction

Only a single .blend file can be edited at a time.

Hint

As with the application it’s possible to start multiple instances, each with their own bpy and therefor Blender state. Python provides the multiprocessing module to make communicating with sub-processes more convenient.

In some cases the library API may be an alternative to starting separate processes, although this API operates on reading and writing ID data-blocks and isn’t a complete substitute for loading .blend files, see: