Lantos3D: Python tipps and tricks

Class Attribute vs. Instance Attribute

I will show what is the difference between class and instance attribute. If you have some instances the class attribute will be affected by all of them, but the instance attribute just by the own instance.

   
       class
       Name
       ():
      
       count = 0
      
       def
       __init__
       (self, name):
      
       self
       .name = name
      
       Name.count += 1
       
       man1 = Name('David')
      
       man2 = Name('Jozsi')
      
       print Name.count
      
       # Result: 2 #
      
       print man2.name
      
       # Result: 'Jozsi' #

Lambda function bug

Sometimes the lambda function does not want to work. You do everything on right way but you've got error.

   
       # If it's not working:
      
       lamda
       x: call_function()
      
       # Try this:
      
       lamda
       : call_function()

For statement an other way

Today I learnt a new way to use 'for' statement. It is really useful if we want to give a simple function to every item:

   
       # We have a list
      
       lst = ['a_1', 'b_2', 'c_3']
      
            numbers = [str.split('_')
            for
            str
            in
            lst]
      
       # equivalent with this:
      
       numbers =
       map
       (
       lambda
       str: str.split('_')[1], lst)

Map function

There is the "map" function in pyton that is very handy. I show how it works.

   
       # Example 1.
      
       # We define a function first.
      
       def
       myFunction
       (input): return input+1
      
       result =
       map
       (myFunction, [1,2,3,4])
      
       print result[1]
      
       # Result: 3 #
      
       # Example 2.
      
       map
       (
       lambda
       x : x+1, [1,2,3])
      
       # Result: [-1, 1, 3] #

"map(f, sequence)" is directly equivalent with: "[f(x) for x in sequence]"

Class inheritance

I wrote a little template for class inheritance with super function.

class A (object):

def __init__ ( self , name= 'alma' , *args, **kwds):

super (A, self ).__init__( *args, **kwds )

self .name = name

def getName ( self ):

print self .name

class B (A):

def __init__ ( self , number=12 , *args, **kwds):

super (B, self ).__init__( *args, **kwds )

self .number = number

def getNumber ( self ):

print self .number

b_object = B()

b_object.getName()

# Result: 'alma' #

SetAttr command

I wrote a script some days ago and I had a problem with cmds.setAttr's keyable flag. If you want to lock and hide a double3-type-attribute you need to set separately each attribute.

# Wrong:
cmds.setAttr('pCube1.t', k=False)
# Correct:
for axis in ['x', 'y', 'z']:
cmds.setAttr('pCube1.t'+axis, k=False)

23 Jun 2012

Python tipps and tricks