RE: [Maya-Python] Basic question about pyMel
br...@meljunky.com
-------- Original Message ----------
Subject: [Maya-Python] Basic question about pyMel
From: Simon Davies <simonj...@hotmail.co.uk>
Date: Mon, March 23, 2015 12:59 pm
To: python_in...@googlegroups.com
Hi all,I understand that if I import pyMel into Maya like this:
I can then build up pyMel functions like this:
However if I import pyMel with a name space instead:
The above code doesn't work, so how should it be written if I import pymel as pm?Thanks a lot.
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Marcus Ottosson
Though Brian is right, it doesn’t quite explain why you are getting the behaviour you’re seeing.
It’s a very good question, and I can completely understand why you would expect to prefix each PyMEL related call with pm as that is what you imported it as. The reason you don’t is a tad complicated, but has to do with two things.
- Scope
- Object Oriented Programming
Scope has to do with what variable names you can call without referencing anything else.
>>> my_variable = 5
>>> print my_variable
5
>>> import os
>>> print os
<module 'os' from 'C:\Python27\lib\os.py'>
The object-oriented part on the other hand is responsible for allowing you to call upon members of a variable; which in this case would instead be called an object.
>>> my_variable = "hello"
.>> print my_variable.upper()
HELLO
And that has to do with the dot following a variable. The dot is essentially saying “run the following command within the scope of the previous variable”. In this case, the variable is a string-object, and the string is an instance of a class with a method called upper() inside of it.
# Looks something like this.
class String:
def upper(self):
...
If you were to make your own class, you could do the same.
class MyClass(object):
def __init__(self, value):
self.value = value
def plus_one(self):
return self.value + 1
myobject = MyClass(5)
print myobject.plus_one()
# Which would print 6
Objects returned by PyMEL works just like this, which is why you can call upon methods of those objects, without prefixing them with pm.
Does that help?
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Justin Israel
Just think of it like a directory structure.
If you import *, you are putting everything in your "current directory". If you import with a namespace, everything is under a "new directory". The only thing that changes is that leading namespace. Prefer the later and "keep your directory clean" with a namespaced import.
Justin
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Simon Davies
So in my example this part of the code:
pm.ls(type='camera')[0]
is an instance of a class and that class contains the "getParent" and "getTranslation" methods, which means that the instance has access to those methods.
Marcus Ottosson
You’ve got it. :)
In this case, you’re getting instances of a class called Camera, which has a number of parent classes, each adding additional methods to the Camera class.
>>> camera = pm.ls(type='camera')[0]
>>> camera_class = type(camera)
>>> camera_superclasses = camera_class.__mro__
>>> print camera_superclasses
(<class 'pymel.core.nodetypes.Camera'>,
<class 'pymel.core.nodetypes.Shape'>,
<class 'pymel.core.nodetypes.DagNode'>,
<class 'pymel.core.nodetypes.Entity'>,
<class 'pymel.core.nodetypes.ContainerBase'>,
<class 'pymel.core.nodetypes.DependNode'>,
<class 'pymel.core.general.PyNode'>,
<class 'pymel.util.utilitytypes.ProxyUnicode'>,
<type 'object'>) #
That is why this particular instance has so many members for you to call.
>>> dir(camera)
['activeColor',
'addAttr',
'addBookmark',
'addChild',
'addPrefix',
'applyBookmark',
'attr',
'attrDefaults',
'attrInfo',
...
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