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Re: Loading modules from files through C++

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On 05/17/2014 05:49 PM, Stefan Behnel wrote:
> Roland Plüss, 17.05.2014 17:28:
>> On 05/17/2014 04:01 PM, Stefan Behnel wrote:
>>> Roland Plüss, 17.05.2014 15:49:
>>>> On 05/17/2014 03:26 PM, Stefan Behnel wrote:
>>>>> Roland Plüss, 17.05.2014 15:00:
>>>>>> On 05/17/2014 01:58 PM, Stefan Behnel wrote:
>>>>>>> Roland Plüss, 17.05.2014 02:27:
>>>>>>>> I'm using Python in an embedded situation. In particular I have to load
>>>>>>>> python scripts through a memory interface so regular python module
>>>>>>>> loading can not be used. I got working so far a module loader object
>>>>>>>> I've added using C++ to sys.meta_path . Now I'm totally stuck at the
>>>>>>>> finally loading step.
>>>>>>>>
>>>>>>>> I've got this a C++ loader method "load_module(fullname)" which does
>>>>>>>> load the requested module script files into a null-terminated string. I
>>>>>>>> know that "load_module" has to return the module PyObject*. But I can't
>>>>>>>> get the python source in the c-string into a module PyObject*.
>>>>>>>> [...]
>>>>>>>> Can anybody help how in gods name one is supposed to create a module
>>>>>>>> from an in-memory c-string when called from within load_module (or
>>>>>>>> anywhere)?
>>>>>>> Looks like you want to implement a SourceLoader:
>>>>>>>
>>>>>>> https://docs.python.org/3.4/library/importlib.html#importlib.abc.SourceLoader
>>>>>>>
>>>>>>> I recommend implementing this in Python code instead of C code, though.
>>>>>>> Much easier. Cython can help with the integration between both.
>>>>>> That doesn't work in 2.x, doesn't it?
>>>>> Is there a reason you have to use Py2?
>>>>>
>>>>> Anyway, PEP 302 predates Py3 by a couple of years:
>>>>>
>>>>> http://legacy.python.org/dev/peps/pep-0302/
>>>> I'm willing to go to Py3 but only if the solution to the problem is
>>>> simpler than getting it fixed in Py2. So some questions first:
>>>>
>>>> - does this importlib stuff you showed there apply to C++ land (I need
>>>> to fully drive it from C++ not Python code)?
>>> As I said, implementing this in Python code is much simpler than doing it
>>> in C/C++ code. Basically, stop where you got the C string and do the rest
>>> in Python. All your C code has to do is to take a module lookup request
>>> from your custom Python module Finder and return a byte string with the
>>> code. Then let your Python code wrap that in a Loader and return it to the
>>> import machinery.
>> I don't get how this is supposed to work. I'm running it as fully
>> embedded Python. There is no main script. The builtin modules are added
>> as C++ bound classes and a user made main script is loaded but not run
>> directly (I'm hooking into a create object). For this purpose I load the
>> script module using C++ code using PyImport_ImportModule(moduleName). At
>> this time the module loading code has to kick in already (I've added
>> this one by C++ too before). The problem is now that in this call I end
>> up in my C++ loader version where there is no Python script involved. I
>> came to the conclusion that I can solve this only by having the C++ end
>> properly load the module. I could add Python code with
>> PyRun_SimpleString but then I'm down to the same problem as before: how
>> to evaluate code so it is attached to a module or type-class? As I
>> understand it the problem is the same as before just pushed around a bit.
> No, just run some Python code (using PyRun_SimpleString() if you have to)
> and let it do whatever you like. Such as, defining a Finder class and
> injecting it into the import hook. Just provide it with the entry point of
> your C++ loader as a (CFunction) object when you execute it, and then let
> it call that function at need whenever the Finder gets executed.
>
> Alternatively, compile your Python integration code with Cython and link it
> into your main program as yet another binary extension module.
>
> Stefan
>
>
I'm not using Cython so that's out of question. Concerning the injection
how would this work? From the PEP I assume it would have to look like this:

# CODE #
import sys
class VFSModuleLoader:
   def find_module(fullname, path=None):
      return self if VFS.exists( vfsPathFromFullname(fullname) ) else None
   def load_module(fullname):
      sourceCode = VFS.read( vfsPathFromFullname(fullname))
      ???
# CODE #

How does ??? work? If I use "eval" I end up with the code inside
VFSModuleLoader.load_modules as context but it should go into the global
context as an own module.

-- 
Yours sincerely
Plüss Roland

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Re: Loading modules from files through C++ Roland Plüss <roland@rptd.ch> - 2014-05-17 18:28 +0200

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