Python For Maya: Artist Friendly Programming

No developer comes into this world magically knowing every command that Maya has. Well maybe someone does, but it would be an odd skill for a baby to have.

So instead, for the rest of us mere mortals, there's some pretty good documentation about each Maya command and we'll go over how to look up and read this documentation.

The LS command is used to list objects in the scene, and you can give parameters to it to narrow down the list it gives back.

In this video we'll go over how to use the ls command properly to get back just the items we care about.

If Statements are powerful ways to control our logic so that we only run parts of our code when certain conditions are met.

For example, we wouldn't start a party without some sweet tunes, so in Python we could tell it to only do it if the music is there.

Indentation

An important thing to note here is that Python handles two different kinds of indentation:

• 4 spaces
• 1 Tab

Spaces are always preferred. Anyone who says otherwise is a loony. Sometimes you will be changing someone elses code that uses tabs instead of spaces. That is the only time I can recommend tabs, but I also recommend cursing at them.

Fortunately, PyCharm by default converts tabs to spaces, so you won't be hitting a space bar multiple times. Just hit the Tab key once, and it will add 4 spaces. It is also smart enough to understand the current code, and do the best behavior accordingly.

IMPORTANT: Never mix tabs and spaces. It's a world of pain. Use one or the other, and most good editors will let you use tabs, but convert it to spaces for you.

For Loops are another core programming principle. They let us run the same logic for every item inside of a collection (lists, dictionaries, sets, tuples etc..).

Noone wants to write the same code for every single item in a list, especially when some lists can be thousands or millions of items long. So we use a for loop to tell python to run it on each item sequentially. 

While Loops are like the child of the if statement and for loop.

They run as long as a condition is met. These are useful when you don't know exactly how many loops you need to run, but you know that when the condition is met, that you can stop.

Think of looking for your keys. You don't know how many times you'll walk around the house looking for them, but once you find them you know you can stop.

Often, we need to know the type of the object in Maya. Are we dealing with a joint, a mesh or something else entirely? This is probably one of the most common things to do in Maya and in this lesson we'll go over how to find what kind of object you have.

The desired behavior is that if an object has no other children other than it's own shape, then we'll give it a suffix that represents it's shape type, but if an object has multiple children, we'll treat it as if it's a group. This also applies if a geometry object has children because it has a mesh shape as a child as well.

You can find the source code link in the resources.

In case you do want to always rename an object by it's shape type, then please make the following change:

    # Add the shapes=True to only get its shape children
    shapes= cmds.listRelatives(obj, children=True, shapes=True) or []

    # If there were shape children, get the type of the shapes
    if shapes:
        objType = cmds.objectType(shapes[0])
    else:
        # otherwise get the object type of the object itself
        objType = cmds.objectType(obj

If Statements are cool, but what if you have multiple conditions you want to check for? Or if you want to tell Python to do something if the condition isn't met?

Like if we can't start the party then lets go to sleep. Similarly we can tell Python what to do quite easily when different conditions occur. 

NOTE: There is a bug in the latest version of PyCharm that doesn't let you set mayapy.exe as the Python interpreter. Fortunately it's not completely necessary and you can skip that part, and simply add the completion files as shown in this video. I will file a bug report with Jetbrains to get this sorted.

So as much as I like the Maya script editor, it's kind of a drag when your script becomes larger than a few lines of code.

This is where PyCharm comes to the rescue. Not only is it great for large code, it also gives you ton of help while coding. It's a programmers best friend.

In this lesson, we'll go over the proper setup of PyCharm for Maya.

In this lesson we'll go over containing our code within functions for easy use.

Functions are another core principle of programming. They're basically commands that you're telling the computer to run, and they can take optional details called arguments or parameters. 

For example, you ask Dave to get you apples, but you can also tell him how many apples to get. The getting of the apple is a function, and how many is the parameter. 

We'll now go over Dictionaries which are a type of object in Python used to store relationships. 

A real world Dictionary (think Oxfords Dictionary) stores the relationship between a word and it's definition. Similarly Python dictionaries store the relationship of a key and a value, where the word is the key and the definition is the value. 

Python has many, many, many ways to combine words together to make sentences or other words. This is called String Formatting and it's probably the thing I spend the most time doing at work.

There are multiple ways to format strings in Python and I'll go over all the ones that work in Python 2. There are actually more ways in Python 3.6, but we're limited to Python 2.7 for Maya

Variables in Python have a scope. Scopes are the life span of a variable, and when they reach the end of their scope they are cleaned up.

A real world analogy would be of a candy bar. When you are done eating it for desert, you throw it away. In this case, the candy bar is the variable and the desert is the scope. You can't use the candy bar before desert or your mom will get mad at you, and once it's thrown away you don't want to be sorting through the garbage.

So far we've been starting our scripts inside of Maya. This video instead goes over how to create our scripts in PyCharm instead and then access them in Maya.

Now lets create the gear itself!

We'll learn to:

• Create the pipe for the base of the gear
• Select the faces that will become the teeth of the gear
• Extrude those faces

The code for this video is available in the resources.

So we've got a gear, but the director wants to change all the pretty gears we've worked so hard to make.

We could delete them all, OR, we could modify them to match his new visionary idea for more teeth on the gears.

In this lesson we'll go over modifying the gears we created.

Code is here: https://github.com/dgovil/PythonForMayaSamples/blob/master/gearCreator/gears1.py

Classes are a way in Python to create a custom object type. Just like we have a string, an integer, a float etc..., we can have our custom object types that define a way to interact with them.

Now that we've learned about how amazing Classes can be (when used judiciously), we can go on to converting our functions into a Gear class.

Code is available in the resources for this lecture.

Maya has a few different libraries we can use for making user interfaces. Largely they all now use the same library under the hood (Qt) but these are the 4 different ways to access it:

• Maya cmds has a subset of Qt that you can use from Python or Mel.
• Qt is a C++ library that you can you use from C++
• PyQt and PySide are Python wrappers for Qt so that we can use Qt from within Python directly.

This project will use Maya cmds, since a lot of maya code uses it, but the next few will switch over to PyQt/PySide instead.

Before we get into writing our UI, it's always important to write the logic for it first. This lets us test the logic without the UI to see if it's working on its' own, but also it means that other tools can use our functions without needing to use our UI.

So for that reason, we'll start our project by writing the Tween Function to add keys inbetween other keys.

This is the first of two videos in which we'll be getting the time and object selection from Maya so we have the necessary information to perform our tween.

Now that we have our time and object selection, we can figure out how to calculate the value of the key that we'll be placing.

In this video we'll go over:

• Querying Keyframe values on other frames
• Calculating the value of our keyframe
• Setting a keyframe

With our logic out of the way, lets make our User Interface so we can simply drag a slider to set the value of the inbetween key.

It's a lot of work to create a user interface, and we have to repeat that each and every time we make one. If only there was a way to reuse our code! The answer is : Classes!

In this lesson we'll go over taking the code from our TweenerUI and sharing it with a new UI for our Gear Creator

This short lesson shows how to add scripts to the Maya shelf so that you can access them easily without using the script editor each time.

Qt has a long history in earning itself a spot as the most popular cross platform UI library around. Seriously, it's amazing.

Anyway I figure it's good to know why it exists, and why we need it, so this lesson goes over exactly that.

Okay so we know what Qt is, and we've used cmds, but I really want to drive home why you should prefer using Qt where ever possible.

"If it walks like a duck, sounds like a duck then it must be a...."

This is a bit of a digression. I've mentioned Duck typing and it isn't about hitting your keyboard like a duck (How would a duck type anyway?).

Duck Typing is a concept in many programming languages that support Classes, where different classes can behave the same so you can use them in a similar manner without having to know what it is.

Whereas cmds requires you to know what type each UI element is in case you need to modify it, Qt objects let you modify them directly without needing to know what they are.

If you're writing Qt interfaces for Maya, you have a problem today. There are 4 different ways to use Qt, and neither is a clear winner.

• PySide comes with Maya 2011 -  Maya 2016 and uses Qt4
• PyQt4 also uses Qt4 and is often nicer than PySide but doesn't come with Maya.
• PySide2 comes with Maya 2017 and above and uses Qt5
• PyQt5 again uses Qt5, but doesn't come with Maya but is nicer than PySide2 to use.

Additionally each of them do things slightly differently. It can be quite hard to support them all. Or Not.

There's a library called Qt.py that lets you just use it, and it takes care of all the differences for you so that you can sleep peacefully at night knowing your code is safe and sound.

A link to Qt.py is available in the resources for this lecture.

NOTE: In the video I say to use the direct download from Github. Instead, use the releases page: https://github.com/mottosso/Qt.py/releases

This will give you a more stable release than the one from the main page. I'll reupload the video soon with the changes, but just want to make that note here first.

Okay, now we know what Qt is....how do you just get it started? Well first we need to import it and depending on your Maya version this can be different.

This video goes over those differences, so you don't get tripped up when you run into them.

Phew, we have that Qt preamble out of the way, lets get our hands dirty with code.

But we can't start our UI just yet! Remember, we need to make the logic for our code first.

In this video, we'll go over creating the directory to where we'll be saving our controllers.

Now that we have a nice clean directory to save our lovely controllers to, lets go about writing out the code to save our controllers down.

Sweet, our controllers are written to the directory, but now we need to find them so that we can access them.

In this lecture, we'll go over finding files on your computer using Python.

We've saved our controllers, we've found them and now we need to Load Them!

In this lecture, we'll go over loading back in the controllers we saved down.

Uh Oh! We have a bug in our code! But don't fret, this is super common. I have bugs in my code all the time, it's like a developers right of passage. Heck, some of us have even brought down whole studios with a simple bug (not me though...I swear! )

So lets find our bug, squash it and carry on with our lives!

We may want to write additional data along with our controllers. We can use a file format called JSON which is a very common data storage format to store our data.

This lecture goes over writing out the data to JSON and then reading it back in.

Lets also save down some screenshots of our controller so we can know what it looks like.

Hooray, our logic is done! Can we start the UI now? 

Almost, my friend! Before we start the UI, let me show you where you can find help regarding Qt should you get lost.

Yes! Now we can start by showing our window! Never have you seen such a pretty grey box.

In this lecture we'll go over setting up the basis for our user interface, and some common issues that people run into.

We can now start adding interface elements to our window to actually make it useful.

We'll go over adding buttons, textboxes and lists, as well as laying them out in a nice ordered fashion.

Our last video left us with the controllers just being listed out. I want them laid out as a nice gallery of thumbnails though, so in this lecture we'll be going over how to achieve that.

In this short lecture, I'll introduce you to the concept of Signals and Slots in Qt. These are the backbone of how Qt interfaces actually work.

Signals are events that an interface element will say has happened. For example, when a button is clicked, it sends out a signal saying that an event has happened where it has been clicked.

Slots are the other side of a signal. You connect slots to a signal, so that Qt automatically runs that slot when the signal is emitted. Slots are just a fancy name for a function.

Now that you understand the theory behind Signals and Slots, let's use them to connect up our UI so that it can function.

The Light Manager

In this project we'll make a UI to create, manage and edit lights in our scenes. It will also write out the lights and read them back in using just JSON.

We'll learn the following skills:

• Using PyMel and when to use PyMel and when to use Maya cmds
• Making our own custom interface controls in Qt
• Using the OpenMaya API to combine Maya controls with our Qt controls
• Using Anonymous functions with Partial and Lambda
• Using Loggers
• Writing portable code that can be used in any version of Maya

Code is available in the resources for this lecture.

PyMel is another Python library inside Maya.

It can really help clean up your code and make Maya a lot easier to use. It does have several drawbacks in terms of speed and stability so several studios don't allow its use, but it is very useful otherwise and I think it's very useful to learn it.

This project will have less preamble and we'll be jumping right in! 

This lecture covers the following:

• Starting the Qt UI like we did in the previous project.
• Using partial to store values for a function that we'll call later

We need a custom user interface that does more than the built in Qt ones do. Fortunately Qt lets us build our own using other Qt elements.

This lecture covers:

• Creating a custom Qt Widget for our needs by combining other ones together
• Using lambda which is a way to define a single line function without a name.

Often we'll use lambdas for when we don't want to create a whole function because we won't be using it more than the one time, and they're simple by nature.

NOTE: In the video I forget to add the second "QtWidgets.QSizePolicy.Maximum" parameter for the vertical value of "scrollWidget.setSizePolicy".  It should be scrollWidget.setSizePolicy(QtWidgets.QSizePolicy.Maximum, QtWidgets.QSizePolicy.Maximum)

See line 188 here: https://github.com/dgovil/PythonForMayaSamples/blob/master/lightManager/lightManager.py#L188

This lecture  is a continuation of the last one as we finish up the behavior of our custom widget.

This video will cover:

• Creating buttons to hide the lights
• Creating a custom Qt Signal to tell other lights to hide instead
• Making a slider to control our light intensity

In this video we'll continue from where we left off and add the ability to change the color of our light.

We'll go over:

• Calling Maya's color picker from Qt
• Using Qt Stylesheets to style our color button
• Converting between different color ranges

This lecture covers two important topics:

Portable Code

Unfortunately, like we learned earlier, the different Qt libraries have some differences, and while Qt.py tries its best to handle them all, there are a few it can't.

This lecture goes over writing code that can work across all Qt libraries. 

You likely won't need this, and likely have chosen to stick with just one. Still, I cannot predict which one you chose as it depends on your setup and Maya version, so this video will cover all of them so you can pick the bits you need.

Loggers

Python has a great way of controlling what information gets reported by using loggers. These are like print statements on steroids that you can enable and disable across your code very easily.

Another Python fundamental is Try and Except. This concept lets us say that we should try something out, and if it doesn't work, then do something else.

For example if you try to eat a pie and it's too hot, you'll instead go and drink water rather than stop and be in pain.

Now that our Light Manager is pretty complete, we want to be able to save our lights down as a JSON file that we can share with other people.

In this lecture we'll go over doing just that.

We've saved down all these light rigs as JSON files, but we need to be able to read them back in to Maya so that we can load back our old lighting setups or use some that other people have built.

Continuing on from our last video, we'll now go over:

• Renaming files
• Duplicating files
• Using regular expressions (a.k.a regex) to use name patterns to be more particular in how we rename our files.

While we've covered several of the most common libraries you will be using, we haven't been able to fit in two other common libraries.

Sys

Sys is a module in python that lets you access system information, including the version of Python being run, what modules are loaded and where Python will look for other modules.

Subprocess

Subprocess lets you launch external applications from Python. This is really useful for example to call preexisting applications rather than having to redevelop your task in Python, or just launching an application for your user.

e.g. We can launch an image editor to edit the screenshots we save out in the Controller Library project

This course has used PyCharm as its' primary editor, but there are many others out there.

In this video, I'll go over a few of the more popular options.

Sublime text is one of my favorite editors other than PyCharm. It's weird that people have favorite editors, but when you're working in them all day, you kind of develop that.

This lecture goes over setting up Sublime Text for Maya.

Eclipse is also another common editor that can be setup to work with Maya. I'm not it's biggest fan, but you might work in a studio that uses it so I'll leave this little guide to setting it up.