lambda and map in Maya

Starting using a couple shorthand techniques today via map and lambda to save on screen real estate when authoring Python modules in Maya.  I often times will troll the scene for info and want to print stuff:

Here, I find the transform name for all mesh in the scene, then print them all with tabs in front:

import sys
import maya.cmds as mc
# Get transform for each mesh:
shapes = mc.ls(type='mesh')
transforms = map(lambda x: mc.listRelatives(x, parent=True)[0], shapes)
# print with tab in front:
map(lambda x: sys.stdout.write('\t%s\n'%x), transforms)

By using our map / lambda combo, I’m able to side-step the need to write any loops. Here’s how it would look otherwise:

import maya.cmds as mc
# Get transform for each mesh:
shapes = mc.ls(type='mesh')
transforms = []
for s in shapes:
    transforms.append(mc.listRelatives(s, parent=True)[0])
# print with tab in front:
for tran in transforms:
    print '\t', tran

Not counting imports and comments, I halved the number of lines of code. One could argue the bottom example is possibly more readable however.

openFrameworks + Code::Blocks Install
Uninstance all instances in a Maya scene
2010
06/14
CATEGORY
CG
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3 comments
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  • Comments (3)
    • Pat Corwin
    • June 17th, 2010 11:26pm

    Even better than lambda/map is list comprehension (at least for me). The format is:
    [ for in if ]
    Thusly the above example would be replace:

    transforms = map(lambda x: mc.listRelatives(x, parent=True)[0], shapes)

    with

    transforms = [ mc.listRelatives(x, parent=True)[0] for x in shapes ]

    An example of using an option condition is might be to only get meshes suffixed with “Ctrl”

    transforms = [ mc.listRelatives(x, parent=True)[0] for x in shapes if mc.listRelatives(x, parent=True)[0].endswith(“Ctrl”) ]

    I like how it’s basically the same loop syntax and readability in one line. While you could do that for the last line (or include tabs in first loop), the trick I like to use instead is:

    “\n\t”.join(transforms)

    Which is essentially the reverse of .split. It takes a list and joins all the items with the given string. You’ll need to indent the print since the first item won’t have the tab but this is a nice way to print lists quickly since it’s only one print instead of several.

    • Pat Corwin
    • June 17th, 2010 11:45pm

    Blarg! Because some of code my previous comment were interpreted as html tags, the format for list comprehension is:

    [ (result) for (iter variable) in (something iterable) if (optional condition) ]

  3. I agree comprehensions are great :) And you’re right: Using a list comprehension actually does give you a more control over querying the shapes using the condition. I wonder which is faster though? 😉 Thanks for the tip.

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