Easiest way to access C module in Python

[Chris Angelico]

On Tue, Nov 7, 2017 at 12:52 PM, bartc <bc at freeuk.com> wrote:
> On 07/11/2017 00:58, Chris Angelico wrote:
>>
>> On Tue, Nov 7, 2017 at 10:43 AM, John Pote <johnpote at jptechnical.co.uk>
>> wrote:
>>>
>>> Hi all,
>>> I have successfully used Python to perform unit and integration tests in
>>> the
>>> past and I'd like to do the same for some C modules I'm working with at
>>> work. There seem to be a number of ways of doing this but being busy at
>>> work
>>> and home I looking for the approach with the least learning curve.
>>>
>>> I don't want to add the C modules into the CPython build itself as I've
>>> never done this and at work it's a real pain getting admin rights to do
>>> this, and when you do it lasts just 24 hours. The C modules are likely to
>>> change frequently as bugs are found and features added.
>>
>>
>> Fortunately, you don't have to modify CPython to do this :)
>>
>>> The other option I'm considering is to use sockets and write a C wrapper
>>> round the C modules I want to test. This has the advantage for me that I
>>> know about sockets from Python & C points of view and I get complete
>>> control
>>> of the C compile process. This may be important as the C modules come
>>> from
>>> an embedded project and I don't want to change them in any way.
>>>
>>> Are there any other approachs to this problem?
>>> I'll be using Python 3.5 (work) and 3.6 (home).
>>> Feedback appriciated.
>>
>>
>> This. The best way to do this is to create a wrapper... but the best
>> way to create that wrapper is with Cython. (Not to be confused with
>> CPython.) Check out http://cython.org/ to see what it takes to carry
>> information into and out of the C module. You'd compile the Cython
>> wrapper and then import that from Python directly.
>
>
> Cython seems very confusing to me.
>
> The simplest way for Python to run C is for Python to just run the
> executable created using C. If that is possible.
>
> Otherwise what /I/ would look for is ways to call C functions inside shared
> libraries (.dll and .so). That requires that the modules under test be
> wrapped as a shared library, which may be extra effort (but it will still be
> using C, so with familiar tools and no crossover with Python at this point).
>
> To call shared library C functions from Python I think involves the ctypes
> module (I've never done it). Googling 'ctypes shared library' gives some
> promising results.

The point of Cython is to make this easier. It's worth learning.

ChrisA