VTK::WrappingPythonCore

Python Wrapper Core Classes

This directory provides the core support classes that are used by VTK’s Python wrappers. The classes can be split into two broad categories: the PyVTK classes provide C APIs for Python types, while the vtkPython classes are C++ utility classes.

The Python Classes

PyVTKObject

This defines APIs for creating and managing PyVTKClass objects, which are Python extension types that wrap vtkObjectBase-derived classes, and PyVTKObject objects, which are instances of the these extension types.

PyVTKSpecialObject

Similarly, PyVTKSpecialType objects are Python extension types that wrap C++ classes that are not derived from vtkObjectBase, and PyVTKSpecialObject wraps the instances. These object are reference counted on the Python side, but not on the C++ side. In general they are lightweight objects that are cheap to copy.

PyVTKTemplate

These objects represent C++ class templates. The wrappers instantiate the templates over a limited set of template parameters, and PyVTKTemplate is a container for the template instantiations. It is implemented as a dictionary that maps template parameters to template instantiations.

PyVTKEnum

This provides an API for managing subtypes of the Python int type that represent named C++ enum types.

PyVTKNamespace

This provides an API for managing subtypes of the Python module type that represent C++ namespaces.

PyVTKReference

Python does not support C++-style pass-by-reference, but pass-by-reference can be simulated by passing a typed container whose contents can be modified. The PyVTKReference type defines such containers. Within Python, this type can be accessed as vtkmodules.vtkCommonCore.reference.

PyVTKMethodDescriptor

In Python, a method descriptor is an object that customizes method lookup, specifically it customizes object.method and class.method method access. The PyVTKMethodDescriptor customizes the access of PyVTKClass methods. It handles bound method calls, unbound method calls, static method calls, and calls to overloaded methods.

PyVTKExtras

This one is not actually a class, it is a helper function that adds utility methods and types like the previously-mentioned reference type to the vtkCommonCore module. Everything in this file becomes part of vtkCommonCore.

The C++ Classes

vtkPythonUtil

This is a singleton that keeps track of all the vtk-python extension modules that have been loaded, and all of the vtk-python objects that have been instantiated. It contains all of the machinery that is needed for moving VTK objects from C++ to Python and back again.

vtkPythonCommand

This is a subclass of vtkCommand that allows Python methods to be used as VTK observer callbacks.

vtkPythonArgs

When a method call is performed in the wrappers, vtkPythonArgs does the conversion of the arguments from Python to C++, and it also converts the return value from C++ to Python.

vtkPythonOverload

When an overloaded method is called from Python, this class uses the method arguments to decide which overload to use.

vtkPythonCompatibility

This is actually just a header, not a class. It contains macros that make it easier to write code that is compatible with different versions of the Python C API.

vtkSmartPyObject

Whereas the other classes in this directory are for using VTK C++ objects through Python, this class is for using Python objects through C++. This class is a C++ smart pointer that handles Python reference counting.