Editing VTK (section)

===Minimize includes in headers===

The general rule of header files in VTK is that you include only the header file of the superclass.  For everything else, you merely forward declare it in the header.  See [[C++ Development#Minimize includes in headers]] for more info on forward declarations.

This is a good rule to follow where possible in C++ anyways, but in VTK it is particularly important, because many kinds of objects (e.g. STL - Standard Template objects) will cause Python Wrapping of the class to fail if used in the header file.