Python bindings tutorial

Alf P. Steinbach alfps at start.no
Wed Mar 17 13:03:06 CET 2010


* Dave Angel:
> Stefan Behnel wrote:
>> <div class="moz-text-flowed" style="font-family: 
>> -moz-fixed">MikeLisanke at gmail.com, 17.03.2010 10:08:
>>> Its interesting you've mentioned the hard work involved in this
>>> interface (binding to an EXE instead of a DLL). A year or more ago I
>>> was looking at interfacing IPMITOOL to python. Do to the problems
>>> incurred with swig/python I switched to a running the process through
>>> its command-line interface. I always felt the problems in interfacing
>>> python to an EXE should be worked on (to minimize them), making the
>>> direct use of an EXE API's a routine task. I understand some of the
>>> problems using an EXE (not running all of its startup code   but
>>> enough for its proper operation). Have you found this a recurring
>>> question? Thanks.
>>
>> I think the point here is that executable binaries are not supposed to 
>> be used as libraries. Libraries are. That's the difference between a 
>> DLL and an executable in the first place. To run an executable, 
>> execute it. The subprocess module is the tool of choice here. To use a 
>> DLL, link against it.
>>
>> Stefan
>>
> There's no real reason parts of an exe cannot be exported, same as a 
> dll.  They are in fact the same structure.  And in fact many other files 
> in the Windows environment are also the same structure, from fonts to ocx's
> 
> Saying they're "not supposed to be used" is like saying that a python 
> module should not have an
> 
> if __name__ == "__main__":
> 
> section.  After all, who could want to both run a file, and import the 
> same file??

A Windows DLL has defined initialization and cleanup per process and per thread.

This means that e.g. static variables can be properly initialized when you load 
the DLL in order to use its functions (I'm skipping discussion of subtle 
problems, but that's the essence).

A Windows EXE has (only) a single entry point which is for process startup. It 
invokes the EXE's behavior-as-a-program. There is no way to use it to e.g. 
initialize static variables in order to use exported functions.

Hence Mike Lisanke's idea of "not running all of its startup code but enough for 
its proper operation" is generally not possible.

An EXE can be used as a kind of server, /if/ it is designed for that. In 
particular it can be a COM server, allowing access of its functionality from any 
COM-enabled binding, which for Python would mean OLE Automation (COM, OLE, 
Automation: this is Microsoft technology, we're talking Windows EXEs here). But 
a Python binding to EXEs in general can't, as far as I can see, make assumptions 
about any particular kind of server being implemented by the EXE.


Cheers & hth.,

- Alf



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