[Python-Dev] Re: .DLL vs .PYD search order

[James C. Ahlstrom]

Guido van Rossum wrote:
> 
> > I would like to argue that on Windows, import of dynamic libraries is
> > broken.  If a file something.pyd is imported, then sys.path is searched
> > to find the module.  If a file something.dll is imported, the same thing
> > happens.  But Windows defines its own search order for *.dll files which
> > Python ignores.  I would suggest that this is wrong for files named
> > *.dll,
> > but OK for files named *.pyd.
> 
> I think you misunderstand some of the issues.
> 
> Python cannot import every .dll file.  Only .dll files that conform to
> the convention for Python extension modules can be imported.  (The
> convention is that it must export an init<module> function.)

Of course I meant that the test is LoadLibrary(module) followed
by GetProcAddress(h, "init" + module).  Both must succeed.

> This seems logical -- Python extensions must live in directories that
> Python searches (Python must do its own search because the search
> order is significant).

The PYTHONPATH search path is what I am trying to get away
from.  If I eliminate PYTHONPATH I still can not use the
Windows DLL search path (which is superior) because DLLs
are searched on PYTHONPATH too; thus my post.  I don't believe
it is important for Python module.dll to be located on PYTHONPATH.

> > A SysAdmin should be able to install and maintain *.dll as she has
> > been trained to do.  This makes maintaining Python installations
> > simpler and more un-surprising.
> 
> I don't see that a SysAdmin needs to do much DLL management.  This is
> up to installer scripts.  Anyway how hard can it be for a SysAdmin to
> leave DLLs in specific directories alone?

The problem is maintaining PYTHONPATH plus having DLL's on a
non-standard search path.  Yes, PythonDev[:] and professional
SysAdmins can do it.  But it is not as simple as it could be.
Someone has to write the install scripts.  And what if something
doesn't work?  Think of Python being used as a teaching language
for the 8th grade.  Think of the 8th grade teacher trying to get
all this right.  The only thing that works is simplicity.

> But at what point should this LoadLibrary() call be called?  The
> import statement contains no clue that a DLL is requested -- the
> sys.path search reveals that.

Just after built-in and frozen modules.

> I claim that there is nothing with the current strategy.

Thank you for thoughtfully considering and commenting at length
on this issue.  Lets ignore it for the moment.  The other
problems with PYTHONPATH are more pressing.  But if those
issues are solved, this one will stick out.

JimA