This is for everyone who, for whatever reason, are putting off learning Python. Ideally, if you are coming from another language such as MEL or Perl, you should be able to skim through these demos and have no problem transitioning to Pythonic syntax. The following Python snippets are selections from the online documentation at
http://docs.python.org/, which I modified whenever possible to fit into a Maya context.
Data Structures
myString="Hello"
mySecondString="World"
result=myString+mySecondString
myMultilineString="""Hello World.
What a beautiful world it is."""
myRawString=r"C:/Users"
firstLetter=myString[1]
lastLetter=myString[-1]
firstWord=myString[0:4]
- Unicode: Since Maya is used internationally, multiple language packs are supported which require a unicode character set. Think of unicode as the big brother of the standard ASCII model. You will not see anything unusual as the result of MEL commands, however Maya will return Python commands in unicode notation. As long as your in Maya the prefix u can be ignored, however, if you are writing output to a file they will have to be converted to ASCII.
print cmds.ls(cameras=1)
>>[u'frontShape', u'perspShape', u'sideShape', u'topShape']
print cmds.ls(cameras=1)
>>[u'frontShape', u'perspShape', u'sideShape', u'topShape']
myToys=["yoyo", "cup", "ball", "crayon"] #the names of your objects
cmds.select(myToys)
firstToy=myToys[1] #yoyo
numToys=len(myToys) #3
- List Comprehensions: These are used to create lists from any iterable object. The first time I used them was to retrieve the nth column in a matrix stored as vectors.
myMatrix=[[1,2,3,4],[1,2,3,4],[1,2,3,4]]
thirdRow=myMatrix[2] #[1,2,3]
thirdColumn=[x[2] for x in myMatrix] #[3,3,3]
- Tuples: Are similar to list except they cannot be modified, also known as immutable.
myList=["Hello", 1]
myList[1]=5 #can change the value
myTuple=("Hello", 1)
myTuple[1]=5 #ERROR
- Sets: Sets are GREAT. They are just like lists but prevent duplicate elements.
keyLight= cmds.lightlink(light="keyLight", query=1) #return all objects set to receive light from keyLight
backLight= cmds.lightlink(light="backLight", query=1) #return all objects set to receive light from backLight
lightsList=keyLight+backLight #12 items, lists duplicates
lightsSet=set(keyLight+backLight) #8 items, returns only unique elements
- Dictionaries: Sometimes referred to as hashes or associative arrays, are used to store data in name, value pairs.
myCameras=cmds.ls(cameras=1)
myTextures=cmds.ls(textures=1)
myScene={'cameras':myCameras, 'textures':myTextures} #myScene stores all the cameras and textures in the scene
print myScene.keys()
print myScene.values()
print myScene["cameras"]
Control Flow
- While Loops: Use extreme caution when using while loops. There is no way to close Maya if you get caught in an infinite loop.
while x<10:
print x
x+=1 #make sure to terminate the loop!
if (myValue==10 or myValue==20) and myValue!=30
print myValue
elif myValue==0:
print "Cannot be 0"
else: #all occurances
pass #pass keeps Pythonic syntax, useful as placeholders
for x in range(10):
print x, someList[x]
for index, eachItem in enumerate(iterableItem):
print index, eachItem
sphereAttrs=cmds.listAttr('pSphere1')
for eachAttr in sphereAttrs:
print eachAttr+":",
try:
print cmds.getAttr("pSphere1."+eachAttr)
except:
print "Cannot Read"
Functions
def myFunction(arg=None): #defines function myFunction that accepts an argument arg that defaults to None
print arg
return 1
myFunction("Hello World") #calls myFunction
Classes
class newClass():
myInt=5 #class variables
@classmethod #class method decorator
def getInt(cls): #class method
return cls.myInt
def __init__(self, arg): #gets automatically called when an object is instantiated
self.myString=arg #self are instance variables, they are unique per object
def myFunction(self, arg):
print arg, self.myString
myClass =newClass("Hello") #creates a new object from class newClass, objects are instances of a class
myClass.myFunction("World") #Hello World
print myClass.myFunction.myString #Hello
print newClass.myInt #5
print newClass.getInt() #5I hope this will get you all started in the right direction. The vast majority of all your scripts will come from topics discussed here, everything else beyond this cheat sheet will merit a dedicated post. If you have further questions I find it's easiest to just to Google the topic. Even though I am a member of
http://www.python-forum.org/pythonforum/ I rarely, if ever have to create a new thread. On the other hand I highly recommend the Maya Programming Forum on
http://forums.cgsociety.org/ since Maya specifics sometimes get hazy. Hopefully you are all already members.
