I’ve seen two ways of calling superclass methods.

class Subclass(Superclass):
    def __init__(self):
        Superclass.__init__(self)

or

class Subclass(Superclass):
    def __init__(self):
        super(Subclass, self).__init__(self)

and I started wondering about the difference between the two.

The short simple answer is “none”.

The slightly longer answer (Here is the long answer) is that the first method is the only way to go for classic classes, but new-style classes also support the super() builtin (in python 3.0 you can simply call super() without the type and object arguments).

You gain a couple of things with the super() builtin. First, you can change the name of the superclass without having to go into all the overloaded methods to change Superclass to DifferentSuperclass. I have seen code where the same functionality was achieved by simply doing this:

from module import Superclass as BaseClass
 
class Subclass(BaseClass):
    def __init__(self):
        BaseClass.__init__(self)

I find this very confusing having to scroll all the way to the import statements to see the classes superclass, but it has the same effect.

Second, and the really cool thing, is that super() searches all of your classes ancestors to find the method you wan to call. So if you have a complex inheritance scheme you don’t have to know/remember/care which superclass implemented the method you want to call and Python uses it’s MRO (Method Resolution Order) to search the class tree until it finds your method.

For the detailed answer and some examples I highly recommend Raymond Hettinger’s excellent post on the matter just be aware that his examples are using Python 3 syntax.

Today I was trying to get drag and drop working in PyQt and I had the worst time getting it to work. I was trying to have a QListWidget accept file drops which would then add the path to the file to the list. To enable dropping on a widget you must do several things. First of all you must call:

setAcceptDrops(True)

Then you have to implement the following methods:

dragEnterEvent(self, event)
dropEvent(self, event)

What I forgot to do (when I read the docs carefully) is that you also need to implement

dragMoveEvent(self, event)

Which of course makes sense when you think about it. First the cursor enters the widget, then moves within it, then you drop. Simple, right?

And since I couldn’t find an example of this behavior when I was googling (drop file on list, list adds file path) I threw together this example. This example can also reorder the list after you have dragged files on it.

import sys
from PyQt4.QtGui import *
from PyQt4.QtCore import *
 
class MyListWidget(QListWidget):
  def __init__(self, parent):
    super(MyListWidget, self).__init__(parent)
    self.setAcceptDrops(True)
    self.setDragDropMode(QAbstractItemView.InternalMove)
 
  def dragEnterEvent(self, event):
    if event.mimeData().hasUrls():
      event.acceptProposedAction()
    else:
      super(MyListWidget, self).dragEnterEvent(event)
 
  def dragMoveEvent(self, event):
    super(MyListWidget, self).dragMoveEvent(event)
 
  def dropEvent(self, event):
    if event.mimeData().hasUrls():
      for url in event.mimeData().urls():
        self.addItem(url.path())
      event.acceptProposedAction()
    else:
      super(MyListWidget,self).dropEvent(event)
 
class MyWindow(QWidget):
  def __init__(self):
    super(MyWindow,self).__init__()
    self.setGeometry(100,100,300,400)
    self.setWindowTitle("Filenames")
 
    self.list = MyListWidget(self)
    layout = QVBoxLayout(self)
    layout.addWidget(self.list)
 
    self.setLayout(layout)
 
if __name__ == '__main__':
 
  app = QApplication(sys.argv)
  app.setStyle("plastique")
 
  window = MyWindow()
  window.show()
 
  sys.exit(app.exec_())

I have recently been looking at a quite cool program called coral. I recommend you take a look at it. Anyway I’ve put on github a repository of a possibly useful plugin (it’s the same plugin only one is in python and the other one is a compiled one) that can read pc2 caches. *NOTE* the python one requires some changes to the coral source that haven’t made it back to the repo on google code, but that will probably happen at some point. This is mostly there for me version-tracking my code, but you are free to prod at it or *gasp* use it.

coral_plugins on github

I was looking into writing a fairly simple batch file to install some stuff and update environment variables. At some point I wanted to do something like this (constructing a string of ‘;’ separated paths):

set env_vars = \path\to\stuff
if x%user%==xsveinbjorn (
set env_vars = %env_vars%;\another\path
)
if x%hostname%==xgefjun (
set env_vars = %env_vars%;\whoah\this\is\radical
)
echo env_vars

When I would run this I would always get

\path\to\stuff;\whoah\this\is\radical

(Notice that the second path \another\path is missing from the result)
Being very new to writing batch scripts I found this extremely confusing since this sort of stuff would work like a charm in python. So I started the google machine.

The reason this happens is that variables enclosed in ‘%’ are expanded when the script is read, which is quite different from the way python handles this resolving stuff at the last possible time. So when the script is read it will actually look something like this:

set env_vars = \path\to\stuff
if xsveinbjorn==xsveinbjorn (
set env_vars = \path\to\stuff;\another\path
)
if xgefjun==xgefjun (
set env_vars = \path\to\stuff;\whoah\this\is\radical
)
echo env_vars

(I resolved the variables %user% to ‘sveinbjorn’ and %hostname% to ‘gefjun’)
And we can clearly see why we got the result that we got.

So what we have to do is tell the batch file to expand the variables as we go along (something close to how python does things) instead of this expand-it-when-you-read-it nonsense.

To do this we simply have to do three things:

1. Add this line to the top of the code

   setlocal EnableDelayedExpansion

2. Add this to the end of it

   endlocal

3. Replace the enclosing ‘%’ to ‘!’ for the variable you want to delay the expansion for.

   if x%user%==xsveinbjorn (
   set env_vars = !env_vars!;\another\path
   )
   

So my original example would look like this:

setlocal EnableDelayedExpansion
set env_vars = \path\to\stuff
if xsveinbjorn==xsveinbjorn (
set env_vars = \path\to\stuff;\another\path
)
if xgefjun==xgefjun (
set env_vars = \path\to\stuff;\whoah\this\is\radical
)
echo env_vars
endlocal

Now we get the result we were looking for:

\path\to\stuff;\another\path;\whoah\this\is\radical

This also applies to loops and other places where the variable might change between the time you start the batch script and when you actually want to expand it.

Today I was looking at launching programs with some custom environment variables set and if you don’t want to redefine a whole lot of them for this new environment I’d recommend is copying the os.environ dictionary and do your changes on the copy, like so:

new_env = os.environ.copy()
new_env['MEGAVARIABLE'] = 'MEGAVALUE'
subprocess.Popen('path', env=new_env)

Then you should have your program launched with all them fancy environment variables set.

Have you ever called a some scripting function in Softimage and gotten back an XSICollection and printed that return value only to get a ‘None’ value printed to the log?
Don’t worry, you got some data there. Just remember that thats the way python in Softimage prints XSICollections if you would iterate over the collection you will find your values:

for object in returnedCollectin:
   # do something with object
   ...

I have seen some people who just started scripting in xsi run in to this little issue.

This is a simple plug-in command to copy skin weights from one object to another with some significant restrictions:

Download sjtCopySkinWeights

1. The meshes must be exactly mirrors of each other vertex-number wise. This plugin simply uses the vertex numbers of the mesh so each vertex of object A must have a corresponding vertex on object B.
2. The joint names must be somehow side-differentiated e.g. L_joint and R_joint or left_side_arm_JNT and right_side_arm_JNT or you must somehow be able to map one side of joint names to the other.

This has mostly been useful when dealing with hands, you skin one and then you have to copy the weights over, but sometimes maya does a lousy job. This plug-in is pretty much like going in the component editor and copying each value for each vertex between meshes (which would be insane to do by hand).
Note: this is not a very fast script (I was trying to learn the Maya API while writing this) so give it some time to work through dense meshes.

If you have questions or comments just either send me an email or comment below.
 

Usage

1. Select the object with the correct weights.
2. Select the object with the incorrect weights.
3. Run the command e.g. ‘sjtCopySkinWeights -s “L_” -r “R_”‘

Arguments

This command accepts two arguments -search/-s and -replace/-r and each argument requires a string to follow it that tells the plugin how to map the right joint names to the left ones. Yes it works kind of backwards. The command first constructs a list of all the influences on the first object, then it goes over every vertex on the other object and tries to map it’s influences to the ones in the influence-list from the first object.

Example

On one side the joints are called L_….._JNT and the other R_……_JNT the proper arguments for this command to work would be (MEL syntax):

sjtCopySkinWeights -s "L_" -r "R_"

(if no arguments are givien, this is the default search pattern)
This would also have worked (since the search strings can be regular expressions):

sjtCopySkinWeights -s "L_" -r "^[rR]_"

This would allow the right side joints to be named either R_…._JNT or r_…._JNT Just remember the regular expression should go with the -r flag, the -s flag is just used to replace the match from the -r flag with.

Example file

To test the command immediately you can load up th test file included in the zip download ‘copyWeights_example.ma’. First try scrubbing in the timeline to see the difference in weighting. The right side (pCube1) bends in the middle but the left side(pCube2) does not. To copy the weights from pCube1 to pCube2 first load the plugin, select pCube1 then pCube2 and type (MEL syntax):

sjtCopySkinWeights

into the command line (or script editor) and then the weights will have been copied from pCube1 to pCube2. Voila.

This is a tiny snippet I threw together today to speed up selecting the object that was controlling my selected object. In this case the object that was being controlled was a curve, but the constraining object (controlling the curve) was an invisible transform node, so instead of going through the hypergraph I wrote this:

import maya.cmds as mc
selection = mc.ls(sl=1)
toSelect = []
for item in selection:
   constraint = mc.listConnections( item+'.parentInverseMatrix[0]', d=1, s=0,type='constraint')
   if constraint:
      constraint = constraint[0]
      src = mc.listConnections(constraint+'.target[0].targetParentMatrix', d=0, s=1)
      if src:
         toSelect.extend(src)
try:
   mc.select(toSelect)
except:
   pass

Note: this allows you to select multiple constrained objects and this will try and find the driving objects, this does not handle multiple constraints or anything fancy like that. Enjoy

When setting the volume of a quicktime player through COM please keep in mind that the range is from 0-1 NOT 0-100 as I thought (since there doesn’t seem to be any good documentation about the QT COM interface). QT allows you to set the volume to 100 and you end up with painfully loud sound. So set your volume to 1 to allow people to enjoy their hearing for a new day.

When using Maya’s Dope Sheet and Graph Editor you sometimes want to quickly center the editors on the current active frame. You can do this by going ‘View’>'Center Current Frame’ – or – you can add these two commands to your hotkey editor and map that functionality to some spiffy hotkeys:

For the Graph Editor:
animCurveEditor -edit -lookAt currentTime graphEditor1GraphEd;

For the Dope Sheet:
dopeSheetEditor -edit -lookAt currentTime dopeSheetPanel1DopeSheetEd;

For those who like this sort of stuff there is Cameron Fielding’s ‘Tap your timing’ – tip