Python in Maya Done RightPyMEL makes python scripting with Maya work the way it should. Maya's command module is a direct translation of mel commands into python commands. The result is a very awkward and unpythonic syntax which does not take advantage of python's strengths -- particulary, a
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flexible, object-oriented design. PyMEL builds on the cmds module by organizing many of its commands into a class hierarchy, and by customizing them to operate in a more succinct and intuitive way.
Project GoalsCreate an open-source python module for Maya that is intuitive to MEL users and python users alike Fix bugs and design limitations in Maya's python modues, maya.cmds and maya.mel Keep code concise and readable Add organization through class hierarchy and sub-modules Provide documentation accessible via html and the builtin help() function Make it "just work" Production ProvenSince its release over a year ago PyMEL, has accumulated an impressive resume in both feature films and games:
DreamWorks: Fung Fu Panda, Shrek 4, Monsters Vs Aliens, and How to Train Your Dragon Luma Pictures: Pirates of the Carribean: At World's End, Harry Potter 6, and Wolverine ImageMovers Digital: Robert Zemeckis' upcoming A Christman Carol Here's what Seth Gibson of Bungie Studios, makers of the hit game Halo, has to say:
"Having done production python code myself for many years, wrapping my head around Maya's native implementation took a little bit of time. With PyMel, I can think and write the python code and syntax I'm already used to, which speeds up my development time considerably. It's also going to help our other Technical Artists with their Python learning curve, since PyMEL's syntax is consistent with most other python packages. Kudos to the PyMel team for such a well thought out project!"
What's NewAPI HybridizationPyMEL 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 yourobject to change it will automatically be reflected in your python object.
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 LicensePyMEL 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 SupportUnlike 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:
initializes maya.standalone parses your Maya.env and adds variables to your environment sources Autodesk's initialization MEL scripts sources user preferences sources userSetup.mel This makes using Maya in a standalone environment the ideal environment for for batch processes and even rendering.
Tighter MEL IntegrationCalling 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'] = 2Who is PyMEL for?For the NoviceObject-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 ScripterWhen we say PyMEL is concise and easy to read, we mean it.
MELstring $sel[] = `ls -sl`;
string $shapes[] = `listRelatives -s $sel[0]`;
string $conn[] = `listConnections -s 1 -d 0 $shapes[0]`;
setAttr ( $conn[0] + ".radius") 3;PyMELselected()[0].getShape().inputs()[0].radius.set(3)For the Technical DirectorFor 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.
Powerful ClassesNode classes for every node type
camTrans, cam = camera() # create a new camera
cam.setFocalLength(100)
fov = cam.getHorizontalFieldOfView()
cam.dolly( -3 )
cam.track(left=10)
cam.addBookmark('new')An Attribute class organizes all the attribute commands in one place
s = polySphere()[0]
if s.visibility.isKeyable() and not s.visibility.isLocked():
s.visibility.set( True )
s.visibility.lock()
print s.visibility.type()Manipulate file paths with ease
#backup all mb files in the current scene's directory
basedir = sceneName().parent
backupDir = basedir / "backup" #slash op joins paths
if not backupDir.exists:
backupDir.mkdir()
for file in basedir.files( '*.mb' ):
print "backing up: ", file.name
file.copy( backupDir / (file.namebase + ".old") )Work with shape components, perform vector math, and easily set object attributes with the results
#select all faces that point up in world space
s = polySphere()[0]
for face in s.faces:
if face.getNormal('world').y > 0.0:
select( face, add=1)Manage optionVars as a python dictionary
if 'numbers' not in optionVar:
optionVar['numbers'] = [1,24,47]
optionVar['numbers'].append(9)
numArray = optionVar.pop('numbers')PyMEL provides customized operators for succinct scripting:
cam = camera()[0]
sphere = polySphere()[0]
sphere | cam # parent the camera to the sphere
cam.tx >> cam.ty # connect operator
cam.tx // cam.ty # disconnect operatorIncludes Tools to Ease Your Transition to Pythonmel-to-python translator for converting mel script into python scripts python-to-mel plugin factory for turning python classes into mel commands ipymel customized python interpreter
Code Comparisonwith Melstring $objs[] = `ls -type transform`;
for ($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 );
}default Pythonobjs = 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]) )with Pymelfrom 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 proceduresthere's a reason why python is rapidly becoming the industry stanadard. with pymel, python and maya finally play well together.
Pymel is developed in-house at Luma Pictures. [Less]
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