Executing Python from MAXScript

Using Python Libraries in MAXScript

Python libraries can be imported and used in MAXScript, using Python.Import(). In this example, we import the Python built-in methods and constants, and use the pow() function:

bi = Python.Import "__builtin__"
-- <module '__builtin__' (built-in)>
bi.pow 2 3
-- 8

If a module gets dirty (for example, a keyword gets re-defined), you can re-import using Python.Reload():

python.reload bi
-- <module '__builtin__' (built-in)>

Simple Python types, such as int, bool, float, and str, are copied into their corresponding MAXScript types. Complex types, such as lists, tuples, dictionaries and classes, are marshalled through a wrapper object. The properties and functions of the type are accessible by name. For sequence types such as a list, you can iterate using the index. Python lists passed to MAXScript are 1-based.

For example, to create and access a Python tuple:

bi = python.import("__builtin__")
tp = bi.Tuple(#(1,2,3)) --(1, 2, 3)
print tp[0] -- output: 1
bi.type(tp) -- output: <type 'tuple'>

And to create and access a Python dict:

d = bi.dict one:1 two:2 three:3 -- {u'one': 1, u'three': 3, u'two': 2}
d["four"] = 4
bi.print(d["four"]) -- 4

Here is an example of 1-based list passed to back to MAXScript from Python:

str = python.import("string")
mystrlist = str.split("an example string")
mystrlist[1]
-- prints "an"

Limitations

Because of the way Python is wrapped in MAXScript, methods and functions bound to Python execution frames will not work as expected, if at all. Some examples of calls that will not work via Python.import() include:

sys._current_frames
sys._get_frame
module.globals()
module.locals()

Executing Python from MAXScript

You can execute Python commands and statements (can be a single command/expression or a series of statements); or a Python script (for example, a .py script) from within MAXScript. Use the python.Execute and python.ExecuteFile commands respectively, as follows:

python.Execute "print 'hello'"

python.ExecuteFile "demoBentCylinder.py"

If you provide a full path using the ExecuteFile command; for example, as follows; 3ds Max looks for the Python file in the path provided.

python.ExecuteFile @"C:\Program Files\Autodesk\3ds Max 2015\scripts\Python\demoBentCylinder.py"

Otherwise, 3ds Max looks for the Python script under the following directories:

User Scripts directory
User Startup Scripts directory
Scripts directory
Startup Scripts
Windows paths specified by the Path environment variable. To see a list of these directories, enter echo %path% in your command prompt.

For example, 3ds Max would search under the following directories: userscripts\python, userscripts\startup\python, scripts\python, scripts\startup\python, and subsequently the windows paths.

The output of the results from scripts are printed to the MAXScript Listener window.

NOTE: Python scripts run in MAXScript are not thread-safe. Python commands are always executed in the main 3ds Max thread. You should not attempt to spawn separate threads in your scripts (for example, by using the Python threading module).

Python interface methods

The MAXScript Python interface contains methods for using Python in MAXScript. If you run

showinterface python

in MAXScript, you obtain, in the MAXScript Listener, a list of available methods. The following list describes these methods and arguments:

Init(): Loads Python if it is not loaded already.
Execute() and ExecuteFile(): Loads Python if it is not loaded already. Use Init() if you know that you will be using Python, and do not want the delay associated with loading it to occur the first time it is used. You would call python.Init() in a startup script to take the load time hit at startup, rather than while actually using 3ds Max.
Import(): Imports a Python module.
Reload(): Reloads a Python module, for example if it has been re-defined.
GetLastError(): Returns, as a string, the error message associated with the last error encountered while running the Init(), Execute(), or ExecuteFile() methods.
Result codes (enums): When executing Python from MAXScript, the result codes can be the following constants:
- #success
- #pathError
- #initError
- #scriptFileError
- #executeError
throwOnError keyword argument: Controls whether MAXScript throws a runtime exception if an error occurs while running a method. If set to true, you always obtain a return result code of #success because, in all other cases, a runtime exception would be thrown. It would be up to the script writer to make the call within a try/catch in order to handle the exception.