Module API_intro

Module API_intro

The Blender Python API Reference

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Blender (*)

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Introduction:

This reference documents the Blender Python API, a growing collection of Python modules (libraries) that give access to part of the program's internal data and functions.

Through scripting Blender can be extended in real-time via Python, an impressive high level, multi-paradigm, open source language. Newcomers are recommended to start with the tutorial that comes with it.

This opens many interesting possibilities, ranging from automating repetitive tasks to adding new functionality to the program: procedural models, importers and exporters, even complex applications and so on. Blender itself comes with some scripts, but many others can be found in the Scripts & Plugins sections and forum posts at the Blender-related sites listed below.

Scripting and Blender:

There are four basic ways to execute scripts in Blender:

They can be loaded or typed as text files in the Text Editor window, then executed with ALT+P.
Via command line: 'blender -P <scriptname>' will start Blender and executed the given script. <scriptname> can be a filename in the user's file system or the name of a text saved in a .blend Blender file: 'blender myfile.blend -P textname'.
Properly registered scripts can be selected directly from the program's menus.
Scriptlinks: these are also loaded or typed in the Text Editor window and can be linked to objects, materials or scenes using the Scriptlink buttons tab. Script links get executed automatically when their events (ONLOAD, REDRAW, FRAMECHANGED) are triggered. Normal scripts can create (Text) and link other scripts to objects and events, see Object.Object.addScriptLink, for example.

Registering scripts:

To be registered a script needs two things:

be either in the default scripts dir or in the user defined scripts path (see Info window, paths tab);
have a proper header.

Try 'blender -d' to know where your default dir for scripts is, it will inform either the dir or the file with that info already parsed, which is in the same dir of the scripts folder.

The header should be like this one (all double and single apostrophes below are required):

#!BPY

# """
# Name: 'Script Name'
# Blender: 233
# Group: 'Export'
# Submenu: 'All' all
# Submenu: 'Selected' sel
# Submenu: 'Configure (gui)' gui
# Tooltip: 'Export to some format.'
# """

where:

Name is the string that will appear in the menu;
Blender is the minimum program version required to run the script;
Group defines where the script will be put, see all groups in the Scripts Window's header, menu "Scripts";
Submenu adds optional submenus for further control;
Tooltip is the (short) tooltip string for the menu entry.

note:

all double and single apostrophes above are required;
*NEW*: you can "comment out" the header above, by starting lines with '#', like we did. This is not required (except for the first line, #!BPY, of course), but this way the header won't conflict with Python tools that you can use to generate documentation for your script code. Just remember to keep this header above any other line with triple double-quotes (""") in your script.

Submenu lines are not required, use them if you want to provide extra options. To see which submenu the user chose, check the "__script__" dictionary in your code: __script__['arg'] has the defined keyword (the word after the submenu string name: all, sel or gui in the example above) of the chosen submenu. For example, if the user clicked on submenu 'Selected' above, __script__['arg'] will be "sel".

If your script requires extra data or configuration files, there is a special folder where they can be saved: see 'datadir' in Blender.Get.

Interaction with users:

Scripts can:

simply run and exit;
grab the main input event queue and process (or pass to Blender) selected keyboard, mouse, redraw events;
pop messages, menus and small number and text input boxes;
draw graphical user interfaces (guis) with OpenGL calls and native program buttons, which stay there accepting user input like any other Blender window until the user closes them;
make changes to the 3D View (set visible layer(s), view point, etc);
use external Python libraries, if available.

You can read the documentation for the Window, Draw and BGL modules for more information and also check Python's site for external modules that might be useful to you. Note though that any imported module will become a requirement of your script, since Blender itself does not bundle external modules.

Command line mode:

Python was embedded in Blender, so to access bpython modules you need to run scripts from the program itself: you can't import the Blender module into an external Python interpreter. But with "OnLoad" script links, the "-b" background mode and additions like the "-P" command line switch, Blender.Save, Blender.Load, Blender.Quit and the Library module, for many tasks it's possible to control Blender via some automated process using scripts. Note that command line scripts are run before Blender initializes its windows, so many functions that get or set window related attributes (like most in Window) don't work here. If you need those, use an ONLOAD script link (see Scene.Scene.addScriptLink) instead -- it's also possible to use a command line script to write or set an ONLOAD script link.

Demo mode:

Blender has a demo mode, where once started it can work without user intervention, "showing itself off". Demos can render stills and animations, play rendered or real-time animations, calculate radiosity simulations and do many other nifty things. If you want to turn a .blend file into a demo, write a script to run the show and link it as a scene "OnLoad" scriptlink. The demo will then be played automatically whenever this .blend file is opened, unless Blender was started with the "-y" parameter.

The Game Engine API:

Blender has a game engine for users to create and play 3d games. This engine lets programmers add scripts to improve game AI, control, etc, making more complex interaction and tricks possible. The game engine API is separate from the Blender Python API this document references and you can find its own ref doc in the docs section of the main sites below.

Blender Data Structures:

Programs manipulate data structures. Blender python scripts are no exception. Blender uses an Object Oriented architecture. The bpython interface tries to present Blender objects and their attributes in the same way you see them through the User Interface ( the GUI ). One key to bpython programming is understanding the information presented in Blender's OOPS window where Blender objects and their relationships are displayed.

Each Blender graphic element (Mesh, Lamp, Curve, etc.) is composed from two parts: an Object and ObData. The Object holds information about the position, rotation and size of the element. This is information that all elements have in common. The ObData holds information specific to that particular type of element.

Each Object has a link to its associated ObData. A single ObData may be shared by many Objects. A graphic element also has a link to a list of Materials. By default, this list is associated with the ObData.

All Blender objects have a unique name. However, the name is qualified by the type of the object. This means you can have a Lamp Object called Lamp.001 (OB:Lamp.001) and a Lamp ObData called Lamp.001 (LA:Lamp.001).

For a more in-depth look at Blender internals, and some understanding of why Blender works the way it does, see the Blender Architecture document.

Documenting scripts:

The "Scripts Help Browser" script in the Help menu can parse special variables from registered scripts and display help information for users. For that, authors only need to add proper information to their scripts, after the registration header.

The expected variables:

__bpydoc__ (or __doc__) (type: string):
- The main help text. Write a first short paragraph explaining what the script does, then add the rest of the help text, leaving a blank line between each new paragraph. To force line breaks you can use <br> tags.
__author__ (type: string or list of strings):
- Author name(s).
__version__ (type: string):
- Script version.
__url__ (type: string or list of strings):
- Internet links that are shown as buttons in the help screen. Clicking them opens the user's default browser at the specified location. The expected format for each url entry is e.g. "Author's site, http://www.somewhere.com". The first part, before the comma (','), is used as the button's tooltip. There are two preset options: "blender" and "elysiun", which link to the Python forums at blender.org and elysiun.com, respectively.
__email__ (optional, type: string or list of strings):
- Equivalent to __url__, but opens the user's default email client. You can write the email as someone:somewhere*com and the help script will substitute accordingly: someone@somewhere.com. This is only a minor help to hide emails from spammers, since your script may be available at some site. "scripts" is the available preset, with the email address of the mailing list devoted to scripting in Blender, bf-scripts-dev@blender.org. You should only use this one if you are subscribed to the list: http://projects.blender.org/mailman/listinfo/bf-scripts-dev for more information.

Example:

 __author__ = 'Mr. Author'
 __version__ = '1.0 11/11/04'
 __url__ = ["Author's site, http://somewhere.com",
     "Support forum, http://somewhere.com/forum/", "blender", "elysiun"]
 __email__ = ["Mr. Author, mrauthor:somewhere*com", "scripts"]
 __bpydoc__ = """\
 This script does this and that.

 Explaining better, this script helps you create ...

 You can write as many paragraphs as needed.

 Shortcuts:<br>
   Esc or Q: quit.<br>
   etc.

 Supported:<br>
   Meshes, metaballs.

 Known issues:<br>
   This is just an example, there's no actual script.

 Notes:<br>
   You can check scripts bundled with Blender to see more examples of how to
  add documentation to your own works.

"""

A note to newbie script writers:

Interpreted languages are known to be much slower than compiled code, but for many applications the difference is negligible or acceptable. Also, with profiling to identify slow areas and well thought optimizations, the speed can be considerably improved in many cases. Try some of the best bpython scripts to get an idea of what can be done, you may be surprised.

Version: 2.35 - 2.36

Author: The Blender Python Team

Notes:

this documentation was generated by epydoc, which can output html and pdf. For pdf it requires a working LaTeX environment.
the official version of this reference guide is only updated for each new Blender release. But it is simple to build yourself current cvs versions of this text: install epydoc, grab all files in the source/blender/python/api2_2x/doc/ folder of Blender's cvs and use the epy_docgen.sh script also found there to generate the html docs. Naturally you will also need a recent Blender binary to try the new features. If you prefer not to compile it yourself, there is a testing builds forum at blender.org.

Requires: Blender 2.35 or newer.

See Also:: www.blender3d.org: main site, www.blender.org: documentation and forum, www.elysiun.com: user forum, projects.blender.org, blender architecture: blender architecture document, www.python.org, www.python.org/doc

Generated by Epydoc 2.1 on Tue Jan 4 13:43:05 2005

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