                   VTK-Python Package Documentation
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This documents the new Python package structure for the VTK-Python
modules.

Every effort has been taken to keep the changes backwards compatible
so your old code should work without any problems.  However, we
recommend that you use the new package structure.

The file README_WRAP.txt provides a detailed description of how VTK
objects are accessed and modified through Python.


Contents
^^^^^^^^

  Installation

  VTK-Python interpreters

  Structure/Usage
 
  Other VTK related modules

  Backwards compatibility

  Information for packagers

  Common problems

  Reporting Bugs


Installation
^^^^^^^^^^^^

  There are primarily three ways of using the VTK-Python wrappers and
  modules.

    (1) If you are building VTK from source and want to use the
    VTK-Python packages alone, i.e. you don't want to use VTK via C++,
    Tcl, etc., then simply use the "vtkpython" interpreter that is
    built with VTK.  This is a Python interpreter that is linked to
    the relevant VTK libraries and sets the PYTHONPATH internally to
    the correct locations.  So, all you need to do is use "vtkpython"
    instead of "python".  Naturally this will work only if you retain
    your build tree and don't change the directories where VTK was
    built.

    (2) Using the package from the source build without installing it
    system wide and without using vtkpython.  This is most useful when
    you build VTK off a CVS checkout and do not want to install it
    system wide and still want to use the usual Python interpreter.
    This is also useful if you are not the administrator of the
    machine you are using/building VTK on.

     *nix:

      Under Unix the way to do this is to set the LD_LIBRARY_PATH (or
      equivalent) to the directory that contains the libvtk*.so
      libraries.  You must also set your PYTHONPATH to _both_ the
      directory that contains all the libvtk*Python.so files _and_ the
      Wrapping/Python directory.  Under bash/sh something like so
      needs to be done::
    
        $ export LD_LIBRARY_PATH=$VTK_ROOT/lib
        $ export PYTHONPATH=$VTK_ROOT/Wrapping/Python:$VTK_ROOT/lib

      and under csh::

        $ setenv LD_LIBRARY_PATH ${VTK_ROOT}/lib
        $ setenv PYTHONPATH ${VTK_ROOT}/Wrapping/Python:${VTK_ROOT}/lib

      where VTK_ROOT is the directory where your VTK sources are and
      VTK_ROOT/lib is where the libraries are built.  Change this to
      suit your configuration.

     Win32:

      Similar to the Unix approach, set your PATH to point to the
      directory that contains the VTK DLL's and the PYTHONPATH to the
      directory that contains the Wrapping/Python directory and the
      DLL's.


    (3) Installation via distutils to a directory different from the
    build directory.  The file VTK_ROOT/Wrapping/Python/setup.py is a
    distutils script that should install VTK-Python correctly.  It
    should work under *nix, Win32 and possibly other platforms.

    Under *nix please note that you must first run 'make install' to
    install the libraries to system wide directories.  To install the
    VTK-Python wrappers just do the following::

       # cd VTK_ROOT/Wrapping/Python
       # python setup.py install
    
    The usual options for distutils installers are all available.  So
    it is possible to make a non system wide install by using the
    --prefix option.

    If you have trouble with this script or find bugs please mail us
    at <vtk-developers@public.kitware.com> or at
    <vtkusers@public.kitware.com>.


VTK-Python interpreters
^^^^^^^^^^^^^^^^^^^^^^^

  In order to solve some severe problems with running VTK-Python on
  some platforms and compilers a special Python interpreter is
  distributed along with VTK.  This new interpreter is called
  'vtkpython' and is the recommended way of running VTK-Python
  scripts.  If the vanilla Python interpreter is good enough and works
  well for you, please use it.  However if you run into severe
  problems you might want to give vtkpython a try.  Incidentally, to
  see what the problems are with the vanilla Python interpreter on
  some platforms read this thread:
 
http://public.kitware.com/pipermail/vtk-developers/2002-May/001536.html

  Additionally, if you built VTK along with MPI support
  (VTK_USE_PARALLEL and VTK_USE_MPI are true) then another VTK-Python
  interpreter called 'pvtkpython' is also built.  This interpreter
  initializes MPI correctly and is the recommended way to run parallel
  VTK-Python scripts.


Structure/Usage
^^^^^^^^^^^^^^^

  Once the Python packages are installed properly (either system wide
  or by using environment variables) to use the new package structure
  users will just do

    import vtk
    # or
    from vtk import *

  and all the available 'kits' will be loaded - just like with the
  older vtkpython.  The name of the kits is available in the kits
  variable.

    import vtk
    print vtk.kits
    ['common', 'filtering', 'io', ...]

  If the user specifically wants just the classes the Common directory
  imported the user does:

    import vtk.common

  All the kit names are in lowercase.  This is similar to the way in
  which the Tcl packages are split.  Similarly, classes specifically
  in other kits can be imported by using the appropriate kit name.
  Please do note that even when you import vtk.common, the vtk
  namespace will still have all the kits loaded inside it.  Its just
  that vtk.common will have only the classes from the Common
  directory. 


 Valid Kit names
 ^^^^^^^^^^^^^^^

  Required Kits
  -------------

    common, filtering, io, imaging and graphics.

    These are the required kits that you must have to use VTK.  You
    can import all of them using the required module like so:

	from vtk.required import *

    You should have all the required kits in your namespace.  If any
    of them is not importable you *will* get an ImportError.

  Optional Kits
  -------------

    rendering, hybrid, patented and parallel:

    These are the optional kits.  Unlike the Tcl packages importing
    these kits *will not* import all the required kits in as well.
    For the rationale behind this please read this mail and also the
    thread here:

http://public.kitware.com/pipermail/vtk-developers/2001-October/000828.html

    If you don't have a particular optional kit then Python will not
    raise an exception when importing vtk, but if you try loading it
    directly like so:

        import vtk.parallel

    Then you will receive an import error if there was one.  Also, if
    the module exists but there are linking errors you will get a
    LinkError exception.


Other VTK related modules
^^^^^^^^^^^^^^^^^^^^^^^^^

  Apart from the basic VTK functionality there are other useful VTK
  related modules in the package.  There are various widgets for
  different GUI toolkits.  These are available in the various
  sub-directories of the vtk directory.  At the time of this writing
  the following widgets are available.

    gtk -- pyGTK widgets.

    qt -- Qt widgets.

    tk -- The Tkinter widgets.  

    wx -- wxPython widgets.

  The widgets can be used like so:

    from vtk.tk import vtkTkRenderWidget
    # or
    from vtk.gtk import GtkVTKRenderWindow
    # etc.

  To see what widgets are available please look at the various
  directories in the vtk sub-directory.

  Apart from the GUI widgets there is a directory called util.  This
  directory will contain miscellaneous modules that are useful for
  different things.  Again, look at the directory to see what is
  available.

  There is also a test module that allows one to create unit tests for
  VTK-Python.


Backwards compatibility
^^^^^^^^^^^^^^^^^^^^^^^

  All the older modules like vtkpython etc. are still available.  This
  means that all your old code should still run ok.  However, new
  additions like the pyGTK widget will only be available via the new
  package structure.  To illustrate the point consider the
  wxVTKRenderWindow.py module.  To import this you can do either

    from vtk.wx import wxVTKRenderWindow
    # or
    import wxVTKRenderWindow

  The wxVTKRenderWindow and other older modules have been suitably
  modified to use the new structure.


Information for packagers
^^^^^^^^^^^^^^^^^^^^^^^^^

  Sometimes while building RPMS or debs the provided distutils
  setup.py script might not do.  Here is some information for such
  people who are unable to use the setup.py script.

    (1) The entire contents of this directory and its sub-directories
    could be placed in a system wide directory called 'vtkpython' (or
    something else).  Additionally you will need to create a vtk.pth
    that points to this directory.  Lets say you install the modules
    in /usr/lib/python2.1/site-packages/vtkpython.  Then create a
    vtk.pth that contains just one line containing just the word
    'vtkpython' (without the quotes) in it and place that in
    /usr/lib/python2.1/site-packages/.

    (2) You must ensure that the VTK Python libraries are in both your
    PYTHONPATH and in your linkers path.  Under Unix this means that
    the files libvtkCommonPython.so (libvtk*Python.so) are both in
    your PYTHONPATH and in the LD_LIBRARY_PATH (or in ld.so.conf).

    (3) Under GNU/Linux both (1) and (2) are achievable if you do
    something like so:

     Method 1:

      (a) Put all the Python modules in /usr/lib/vtk/python.

      (b) Put libvtk*Python.so also in /usr/lib/vtk/python.

      (c) Add the /usr/lib/vtk/python directory to /etc/ld.so.conf.

      (d) Create a vtkpython.pth in /usr/lib/pythonX.Y/site-packages/
      with the single entry '/usr/lib/vtk/python' (without the
      quotes).

    Alternatively, the following approach might be preffered (this is
    infact exactly what the setup.py script does):

     Method 2:

      (a) Put all the Python modules in 
        /usr/lib/pythonX.Y/site-packages/vtk_python/.

      (b) Put libvtk*Python.so also in /usr/lib/.

      (c) Create a vtkpython.pth in /usr/lib/pythonX.Y/site-packages/
      with the single entry 'vtk_python' (without the quotes).

      (d) Make symbolic links from
      /usr/lib/pythonX.Y/site-packages/vtk_python/ to
      /usr/lib/libvtk*Python.so  i.e.

      # ln -s /usr/lib/libvtk*Python.so /usr/lib/pythonX.Y/site-packages/vtk_python/
   

  This should give you a working VTK-Python setup.


Common problems
^^^^^^^^^^^^^^^

 Most common problems are described in the VTK FAQ available here:

   http://public.kitware.com/cgi-bin/vtkfaq?req=home

 The following lists a few serious problems and their solution from
 the above FAQ.

  Q. Why do I get the Python error -- ValueError: method requires a
  VTK object?
 
  A.  You just built VTK with Python support and everything went
  smoothly. After you install everything and try running a Python-VTK
  script you get a traceback with this error:

   ValueError: method requires a VTK object.

  This error occurs if you have two copies of the VTK libraries on
  your system. These copies need not be in your linkers path. The VTK
  libraries are usually built with an rpath flag (under *nix). This is
  necessary to be able to test the build in place. When you install
  VTK into another directory in your linkers path and then run a
  Python script the Python modules remember the old path and load the
  libraries in the build directory as well. This triggers the above
  error since the object you passed the method was instantiated from
  the other copy.

  So how do you fix it? The easiest solution is to simply delete the
  copy of the libraries inside your build directory or move the build
  directory to another place. For example, if you build the libraries
  in VTK/bin then move VTK/bin to VTK/bin1 or remove all the
  VTK/bin/*.so files. The error should no longer occur.

  Another way to fix the error is to turn the CMAKE_SKIP_RPATH boolean
  to ON in your CMakeCache.txt file and then rebuild VTK. You
  shouldn't have to rebuild all of VTK, just delete the libraries
  (*.so files) and then re-run cmake and make. The only trouble with
  this approach is that you cannot have BUILD_TESTING to ON when you
  do this.

  Alternatively, starting with recent VTK CVS versions (post Dec. 6,
  2002) and with VTK versions greater than 4.1 (i.e. 4.2 and beyond)
  there is a special VTK-Python interpreter built as part of VTK
  called 'vtkpython' that should eliminate this problem.  Simply use
  'vtkpython' in place of the usual 'python' interpreter when you use
  VTK-Python scripts and the problem should not occur.  This is
  because vtkpython uses the libraries inside the build directory.



Reporting Bugs
^^^^^^^^^^^^^^

If you have trouble or spot bugs please let us know at
vtk-developers@public.kitware.com

