cpython/PC/os2vacpp/readme.txt

IBM VisualAge C/C++ for OS/2
============================

To build Python for OS/2, change into ./os2vacpp and issue an 'NMAKE'
command.  This will build a PYTHON15.DLL containing the set of Python
modules listed in config.c and a small PYTHON.EXE to start the
interpreter.

By changing the C compiler flag /Gd- in the makefile to /Gd+, you can
reduce the size of these by causing Python to dynamically link to the
C runtime DLLs instead of including their bulk in your binaries. 
However, this means that any system on which you run Python must have
the VAC++ compiler installed in order to have those DLLs available.

During the build process you may see a couple of harmless warnings:

  From the C Compiler, "No function prototype given for XXX", which
  comes from the use of K&R parameters within Python for portability.

  From the ILIB librarian, "Module Not Found (XXX)", which comes
  from its attempt to perform the (-+) operation, which removes and
  then adds a .OBJ to the library.  The first time a build is done,
  it obviously cannot remove what is not yet built.

This build includes support for most Python functionality as well as
TCP/IP sockets.  It omits the Posix ability to 'fork' a process but
supports threads using OS/2 native capabilities.  I have tried to
support everything possible but here are a few usage notes.


-- os.popen() Usage Warnings

With respect to my implementation of popen() under OS/2:

    import os

    fd = os.popen("pkzip.exe -@ junk.zip", 'wb')
    fd.write("file1.txt\n")
    fd.write("file2.txt\n")
    fd.write("file3.txt\n")
    fd.write("\x1a")  # Should Not Be Necessary But Is
    fd.close()

There is a bug, either in the VAC++ compiler or OS/2 itself, where the
simple closure of the write-side of a pipe -to- a process does not
send an EOF to that process.  I find I must explicitly write a
control-Z (EOF) before closing the pipe.  This is not a problem when
using popen() in read mode.

One other slight difference with my popen() is that I return None
from the close(), instead of the Unix convention of the return code
of the spawned program.  I could find no easy way to do this under
OS/2.


-- BEGINLIBPATH/ENDLIBPATH

With respect to environment variables, this OS/2 port supports the
special-to-OS/2 magic names of 'BEGINLIBPATH' and 'ENDLIBPATH' to
control where to load conventional DLLs from.  Those names are
intercepted and converted to calls on the OS/2 kernel APIs and
are inherited by child processes, whether Python-based or not.

A few new attributes have been added to the os module:

    os.meminstalled  # Count of Bytes of RAM Installed on Machine
    os.memkernel     # Count of Bytes of RAM Reserved (Non-Swappable)
    os.memvirtual    # Count of Bytes of Virtual RAM Possible
    os.timeslice     # Duration of Scheduler Timeslice, in Milliseconds
    os.maxpathlen    # Maximum Length of a Path Specification, in chars
    os.maxnamelen    # Maximum Length of a Single Dir/File Name, in chars
    os.version       # Version of OS/2 Being Run e.g. "4.00"
    os.revision      # Revision of OS/2 Being Run (usually zero)
    os.bootdrive     # Drive that System Booted From e.g. "C:"
                     # (useful to find the CONFIG.SYS used to boot with)


-- Using Python as the Default OS/2 Batch Language

Note that OS/2 supports the Unix technique of putting the special
comment line at the time of scripts e.g. "#!/usr/bin/python" in
a different syntactic form.  To do this, put your script into a file
with a .CMD extension and added 'extproc' to the top as follows:

    extproc C:\Python\Python.exe -x
    import os
    print "Hello from Python"

The '-x' option tells Python to skip the first line of the file
while processing the rest as normal Python source.


-- Suggested Environment Variable Setup

With respect to the environment variables for Python, I use the
following setup:

    Set PYTHONHOME=E:\Tau\Projects\Python;D:\DLLs
    Set PYTHONPATH=.;E:\Tau\Projects\Python\Lib; \
                     E:\Tau\Projects\Python\Lib\plat-win

The EXEC_PREFIX (optional second pathspec on PYTHONHOME) is where
you put any Python extension DLLs you may create/obtain.  There
are none provided with this release.


-- Contact Info

If you have questions, suggestions or problems specifically with
the OS/2 VAC++ port of Python, please contact me at:

    Jeff Rush <jrush@summit-research.com>.

I support no other platform but OS/2 (and eventually AmigaDOS).