VTK/Python Wrapping FAQ: Difference between revisions

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=== Big Picture ===
=== Big Picture ===


All the automated wrapping code generation relies on the consistent coding style followed in the VTK header files and the use of the convenience macros. Specific markers (in comments) in the header mark parts that are not to be parsed (BTX/ETX). Basically, a target language specific parser parses the header file figures out suitable wrapper functions in the desired target language and spits out the wrapper code that is used to generate the wrappings.
All the automated wrapping code generation relies on the consistent coding style followed in the VTK header files and the use of the convenience macros. Basically, a target language specific parser parses the header file figures out suitable wrapper functions in the desired target language and spits out the wrapper code that is used to generate the wrappings.


=== Python Versions ===
The VTK master branch is regularly tested with Python 2.7 and 3.4, and VTK 7 should work with 2.5, 2.6, 2.7, and 3.2+.  Versions of VTK prior to 7.0 will only work with Python 2.


=== Organization ===
=== Organization ===
Line 18: Line 21:


=== Documentation ===
=== Documentation ===
The VTK module for the vtk Python package is all in Wrapping/Python/vtk.  There is a rambling [http://vtk.org/gitweb?p=VTK.git;a=blob;f=Wrapping/Python/README.txt README] in Wrapping/Python that might be of some use. There is also a nice [http://vtk.org/gitweb?p=VTK.git;a=blob;f=Wrapping/Python/README_WRAP.txt README_WRAP.txt] in the same directory that is useful.
 
The VTK module for the vtk Python package is all in Wrapping/Python/vtk.  Individual classes can be inspected with the python "help()" function, e.g. help(vtk.vtkObject).


=== C++ that won't be wrapped ===
=== C++ that won't be wrapped ===
* Templates
* Abstract classes - these are wrapped, and their static methods can be used, but they cannot be instantiated
Because they can't be directly instantiated. Abstract classes are identified as such by putting them in a named list in cmakelist.txt.


* Anything marked as wrap exclude
Information about what kinds of VTK class methods can or cannot be wrapped is provided by the [https://gitlab.kitware.com/vtk/vtk/blob/master/Wrapping/Python/README.md README] file in the VTK/Wrapping/Python directory.  Recent progress on the wrappers is described on the [[VTK/Python_Wrapper_Enhancement |python wrapper enhancements]] page.
This is also done via a named list in cmakelist.txt.
 
* Anything put between //BTX and //ETX in the header file
 
* Methods that take or return unbounded pointers
 
Methods like "GetTupleValue(int i, double *tuple)" aren't wrapped in
python unless they have a signature like GetTupleValue(int i, double
tuple[3]) so that the wrappers know how large the array is.
 
Likewise, methods like "double *GetTuple(int i)" aren't wrapped
unless there is a hint so that the wrappers know how many values will
be returned.
 
The wrappers don't do anything fancy like check how many components an
array has in order to find out what size of tuple to use.  The
wrapping of a method is determined only by the method signature and
the hints in VTK/Wrapping/hints.


== CMake's role ==
== CMake's role ==
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I think all CMake does is to build the parser and organize the building of the generated code, link it correctly (which can be a bloody pain) etc.  I don't think it directly does anything regarding the wrapper generation process.  Any useful CMake macros are best gleaned by looking at CMake files (at least thats how I used to do it).
I think all CMake does is to build the parser and organize the building of the generated code, link it correctly (which can be a bloody pain) etc.  I don't think it directly does anything regarding the wrapper generation process.  Any useful CMake macros are best gleaned by looking at CMake files (at least thats how I used to do it).


=== CMake Macros ===
=== CMake Macros (only valid for VTK 6 and VTK 7) ===
  1. VTK_WRAP_PYTHON3(${NAME}Python KitPython_SRCS "${WRAP_LIST}")
  1. vtk_wrap_python3(${NAME}Python KitPython_SRCS "${WRAP_LIST}")
Will wrap the c++ files in WRAP_LIST into python, outputting a list of
Will wrap the c++ files in WRAP_LIST into python, outputting a list of
transformed files into KitPython_SRCS.
transformed files into KitPython_SRCS.


  2. ADD_LIBRARY(${NAME}PythonD ${KitPython_SRCS} ${Kit_PYTHON_EXTRA_SRCS})
  2. add_library(${NAME}PythonD ${KitPython_SRCS} ${Kit_PYTHON_EXTRA_SRCS})
Will take those outputs, and some optional additional ones, and create
Will take those outputs, and some optional additional ones, and create
a library.
a library.


  3. PYTHON_ADD_MODULE(${NAME}Python ${NAME}PythonInit.cxx)
  3. python_add_module(${NAME}Python ${NAME}PythonInit.cxx)
Will produce a python module that links in the library so that the
Will produce a python module that links in the library so that the
wrapped code is more easily callable via python.
wrapped code is more easily callable via python.
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=== Excluding files from being wrapped ===
=== Excluding files from being wrapped ===
You can tell the wrapper to ignore certain files by using this in your CMakeLists.txt:
For VTK 7 onwards, you can tell the wrapper to ignore certain files by using this in your CMakeLists.txt:
 
  set_source_files_properties(
    vtkMyUnwrappableClass.cxx
    WRAP_EXCLUDE_PYTHON
  )
 
For earlier versions of VTK, you exclude a class globally from wrapping with WRAP_EXCLUDE (which also excludes it from Java and Tcl wrapping).  Or, to wrap a class only in Python but not Java or Tcl, you would mark it as WRAP_EXCLUDE and also as WRAP_SPECIAL.  (The WRAP_SPECIAL property is deprecated from VTK 7 onwards).


SET_SOURCE_FILES_PROPERTIES(
  set_source_files_properties(
   vtkMyUnwrappableClass.cxx
    vtkMyClassWrappableInPython.cxx
   WRAP_EXCLUDE
    WRAP_EXCLUDE
)
  )
    
  set_source_files_properties(
    vtkMyClassWrappableInPython.cxx
    PROPERTIES WRAP_SPECIAL 1
   )

Latest revision as of 23:21, 17 December 2019

VTK Python Wrapping System

Big Picture

All the automated wrapping code generation relies on the consistent coding style followed in the VTK header files and the use of the convenience macros. Basically, a target language specific parser parses the header file figures out suitable wrapper functions in the desired target language and spits out the wrapper code that is used to generate the wrappings.

Python Versions

The VTK master branch is regularly tested with Python 2.7 and 3.4, and VTK 7 should work with 2.5, 2.6, 2.7, and 3.2+. Versions of VTK prior to 7.0 will only work with Python 2.

Organization

  • First look in VTK/Wrapping. Go over the files there. Specifically look at vtkWrapPython.c which actually does the code generation for Python.
  • When VTK is built, an executable called vtkWrapPython is built from this.
  • vtkWrapPython generates the Python wrappers for each wrappable VTK header and this is built to generate the Python wrapper.
  • The wrapper code makes use of Wrapping/Python/vtkPythonUtil.h and several other C and C++ files in Wrapping/Python for various things. Also note that Wrapping/hints is a mechanism for helping the wrapper code with, err, hints to help the wrapping process along. To see what the individual codes represent see Wrapping/vtkParse.y and vtkParse.tab.c
  • The VTK module for the vtk Python package is all in Wrapping/Python/vtk.

Documentation

The VTK module for the vtk Python package is all in Wrapping/Python/vtk. Individual classes can be inspected with the python "help()" function, e.g. help(vtk.vtkObject).

C++ that won't be wrapped

Information about what kinds of VTK class methods can or cannot be wrapped is provided by the README file in the VTK/Wrapping/Python directory. Recent progress on the wrappers is described on the python wrapper enhancements page.

CMake's role

Big Picture

I think all CMake does is to build the parser and organize the building of the generated code, link it correctly (which can be a bloody pain) etc. I don't think it directly does anything regarding the wrapper generation process. Any useful CMake macros are best gleaned by looking at CMake files (at least thats how I used to do it).

CMake Macros (only valid for VTK 6 and VTK 7)

1. vtk_wrap_python3(${NAME}Python KitPython_SRCS "${WRAP_LIST}")

Will wrap the c++ files in WRAP_LIST into python, outputting a list of transformed files into KitPython_SRCS. 

2. add_library(${NAME}PythonD ${KitPython_SRCS} ${Kit_PYTHON_EXTRA_SRCS})

Will take those outputs, and some optional additional ones, and create a library. 

3. python_add_module(${NAME}Python ${NAME}PythonInit.cxx)

Will produce a python module that links in the library so that the wrapped code is more easily callable via python.

That is what ParaView's WRAP_PLUGIN_FOR_PYTHON macro does anyway.

Excluding files from being wrapped

For VTK 7 onwards, you can tell the wrapper to ignore certain files by using this in your CMakeLists.txt: 

 set_source_files_properties(
   vtkMyUnwrappableClass.cxx
   WRAP_EXCLUDE_PYTHON
 )

For earlier versions of VTK, you exclude a class globally from wrapping with WRAP_EXCLUDE (which also excludes it from Java and Tcl wrapping). Or, to wrap a class only in Python but not Java or Tcl, you would mark it as WRAP_EXCLUDE and also as WRAP_SPECIAL. (The WRAP_SPECIAL property is deprecated from VTK 7 onwards). 

 set_source_files_properties(
   vtkMyClassWrappableInPython.cxx
   WRAP_EXCLUDE
 )
 
 set_source_files_properties(
   vtkMyClassWrappableInPython.cxx
   PROPERTIES WRAP_SPECIAL 1
 )
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