API Hybridization

PyMEL 0.9 is a dramatic leap forward in the evolution of python in Maya. The node and attribute classes have been rewritten from the ground up to use the python API as their foundation, increasing the speed and fidelity of PyMEL's object-oriented design.

PyMEL harnesses the API to create a name-independent representation of your object. This means that the annoying inconsistencies of string comparisons are over: no more worrying about short names versus long names, DAG paths, unique paths, instance paths... it's all handled intelligently for you. And what's more, if anything causes the name of your object to change it will automatically be reflected in your python object.

Below, we make a camera, rename it, and then group and instance it, to demonstrate how the name changes are constantly reflected. Keep in mind that the changes could have just as easily been performed by the user interacting with objects through the GUI.

>>> cam, shape = camera()
>>> print cam
camera1
>>> cam.rename('renderCam')
Transform(u'renderCam')
>>> print cam
renderCam
>>> grp = group(cam)
>>> instance(grp)
[Transform(u'group2')]
>>> print cam
group1|renderCam
>>> cam.getInstances()
[Transform(u'group1|renderCam'), Transform(u'group2|renderCam')]

Comparing attributes is just as easy. It doesn't matter what name you use to access an attribute:

>>> cam.t == cam.translate
True
>>> cam.tx == cam.translate.translateX
True

PyMEL node classes now include hundreds of new methods derived from the API, but with the same intuitive and unified design as before. With PyMEL you get the benefits of API speed and versatility without the advanced learning curve.

BSD License

PyMEL is released under the BSD license, which is as open as open source gets. Your studio can freely use, contribute to, and modify this module with no strings attached.

Improved Standalone Support

Unlike the maya module, PyMEL behaves the same in a standalone interpreter as it does in an GUI session. When pymel detects that it is being imported in a standalone interpreter it performs these operations:

1. initializes maya.standalone
2. parses your Maya.env and adds variables to your environment
3. sources Autodesk's initialization MEL scripts
4. sources user preferences
5. sources userSetup.mel

This makes using Maya in a standalone environment the ideal environment for for batch processes and even rendering.

Tighter MEL Integration

Calling MEL from python is still an unfortunate necessity, so PyMEL makes it as easy as possible. This release builds on PyMEL's already vastly improved method, which allows you to call a mel procedure as if it was a python function:

values = ['one', 'two', 'three', 'four']

# default
maya.mel.eval( 'stringArrayRemoveDuplicates( {"'+'","'.join(values)+'"})')

# PyMEL
mel.stringArrayRemoveDuplicates( values )

In the new release, when a MEL script called from PyMEL raises an error, you will get the specific MEL error message in the python traceback, along with line numbers!

For example, here's a procedure "myScript" with a line that will result in an error:

>>> mel.eval( '''global proc myScript( string $stringArg, float $floatArray[] ){
...     float $donuts = `ls -type camera`;}''')

When we call the procedure via PyMEL, we can quickly determine the problem, because PyMEL gives us the error and the line number:

>>> mel.myScript( 'foo', [] )
Traceback (most recent call last):
    ...
MelConversionError: Error occurred during execution of MEL script: line 2: Cannot convert data of type string[] to type float.

Also, getting and setting MEL global variables is accomplished via a special dictionary-like object, which keeps it simple and intuitive:

>>> melGlobals['$gMainFileMenu']
mainFileMenu
>>> melGlobals['$gGridDisplayGridLinesDefault'] = 2

For the Novice

Object-oriented programming, like that provided by PyMEL, is more intuitive to learn because the functionality of an object is directly associated with the object itself. For an artist starting to program in Maya, the first question you might ask is "what can I do with this node?" Using a procedural approach, like that offered by MEL or maya.cmds, you'll have to dig through the hundreds of MEL commands looking for the one that you want. For a camera node, the camera MEL command is easy to find, but did you find orbit, track, dolly, and tumble, which also work on cameras? In PyMEL, all you have to do is type help(Camera) in the python script editor to find out all the things a camera node can do, or just look up the Camera class in the PyMEL docs.

For the MEL Scripter

When we say PyMEL is concise and easy to read, we mean it.

MEL:

string $sel[] = `ls -sl`;
string $shapes[] = `listRelatives -s $sel[0]`;
string $conn[] = `listConnections -s 1 -d 0 $shapes[0]`;
setAttr ( $conn[0] + ".radius") 3;

PyMEL

selected()[0].getShape().inputs()[0].radius.set(3)

For the Technical Director

For those looking to master python in a production environment, PyMEL is more than a module for Maya scripting, it is a repository of example python code -- a self-contained pipeline demonstrating advanced python concepts like function factories, metaclasses, and decorators, as well as essential production practices such as parsing, pickling, logging, and unit testing.

For those who are already masters of python and who naturally expect more out of a python package, PyMEL is for you, too. It was written in for use in production by experiened programmers with a vision for how to add object-oriented design to Maya.

maya.cmds

objs = cmds.ls( type= 'transform')
if objs is not None:                    # returns None when it finds no matches
    for x in objs:
        print mm.eval('longNameOf("%s")' % x)

        # make and break some connections
        cmds.connectAttr(   '%s.sx' % x,  '%s.sy' % x )
        cmds.connectAttr(   '%s.sx' % x,  '%s.sz' % x )
        cmds.disconnectAttr( '%s.sx' % x,  '%s.sy' % x)

        conn = cmds.listConnections( x + ".sx", s=0, d=1, p=1)
        # returns None when it finds no matches
        if conn is not None:
            for inputPlug in conn:
                cmds.disconnectAttr( x + ".sx", inputPlug )

        # add and set a string array attribute with the history of this transform's shape
        if not mm.eval( 'attributeExists "newAt" "%s"' % x):
            cmds.addAttr(  x, ln='newAt', dataType='stringArray')
        shape = cmds.listRelatives( x, s=1 )
        if shape is not None:
            history = cmds.listHistory( shape[0] )
        else:
            history = []
        args = tuple( ['%s.newAt' % x, len(history)] + history )
        cmds.setAttr( *args ,  type= 'stringArray' )

        # get and set some attributes
        cmds.setAttr ( '%s.rotate' % x, 1,  1, 1 )
        scale = cmds.getAttr ( '%s.scale' % x )
        scale = scale[0] # maya packs the previous result in a list for no apparent reason
        trans = list( cmds.getAttr ( '%s.translate' % x )[0] )  # the tuple must be converted to a list for item assignment
        trans[0] *= scale[0]
        trans[1] *= scale[1]
        trans[2] *= scale[2]
        cmds.setAttr ( '%s.scale' % x, trans[0], trans[1], trans[2] )
        mm.eval('myMelScript("%s",{%s,%s,%s})' % (cmds.nodeType(x), trans[0], trans[1], trans[2]) )

MEL

string $objs[] = `ls -type transform`;
for ($x in $objs) {
    print (longNameOf($x)); print "n";

    // make and break some connections
    connectAttr( $x + ".sx") ($x + ".sy");
    connectAttr( $x + ".sx") ($x + ".sz");
    disconnectAttr( $x + ".sx") ($x + ".sy");
    string $conn[] = `listConnections -s 0 -d 1 -p 1 ($x + ".sx")`;
    for ($inputPlug in $conn)
        disconnectAttr ($x + ".sx") $inputPlug;

    // add and set a string array attribute with the history of this transform's shape
    if ( !`attributeExists "newAt" $x`)
        addAttr -ln newAt -dataType stringArray $x;
    string $shape[] = `listRelatives -s $x`;
    string $history[] = `listHistory $shape[0]`;
    string $elements = "";
    for ($elem in $history)
        $elements += """ + $elem + "" ";
    eval ("setAttr -type stringArray " + $x + ".newAt " + `size $history` + $elements);
    print `getAttr ( $x + ".newAt" )`;

    // get and set some attributes
    setAttr ($x + ".rotate") 1 1 1;
    float $trans[] = `getAttr ($x + ".translate")`;
    float $scale[] = `getAttr ($x + ".scale")`;
    $trans[0] *= $scale[0];
    $trans[1] *= $scale[1];
    $trans[2] *= $scale[2];
    setAttr ($x + ".scale") $trans[0] $trans[1] $trans[2];

    // call some other scripts
    myMelScript( `nodeType $x`, $trans );
}

PyMEL

from pymel import *                   # safe to import into main namespace
for x in ls( type='transform'):
    print x.longName()                # object oriented design

    # make and break some connections
    x.sx >> x.sy                      # connection operator
    x.sx >> x.sz
    x.sx // x.sy                      # disconnection operator
    x.sx.disconnect()                 # smarter methods -- (automatically disconnects all inputs and outputs when no arg is passed)

    # add and set a string array attribute with the history of this transform's shape
    x.setAttr( 'newAt', x.getShape().history(), force=1 )

    # get and set some attributes
    x.rotate.set( [1,1,1] )
    trans = x.translate.get()
    trans *= x.scale.get()           # vector math
    x.translate.set( trans )         # ability to pass list/vector args
    mel.myMelScript(x.type(), trans) # automatic handling of mel procedures