Extension modules and common routines in Python/C API
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From: ty ty on 28 Jun 2010 02:16 Hi, folks! I'm writing wrapper for C library. This library consist of several parts. And i want split my extension package into different extension modules. I think, this is the right way ;-) But, there are some common parts that exist in extension package, get_library_version, Error, and so on. I've decided to create additional module, named core, where these routines and variables are defined. And when get_library_version, for example, is used by programmer, Error, in opposite, is used by routines in another modules. As i mentioned in ( above mail), i use create_error for adding new exception class with neccessary fields. Now i call create_error in initcore function, which initialize core module. But, if i don't import package.core, and only import package.module, when package.module.function fails, python's runtime throws error: SystemError: error return without exception set because, Error is not properly initialize in that point. And, if i add: if(!Error) create_error(); in init functions of all my modules, create_error runs several times (for each imported module). I think, i get a different Error every time. I can't check this because of above issue. So, my questions is: how can i organize this pattern? Should i add import package.core in __init__.py in package dir? Or should i create subclass exception of Error in every module? What is the right and pythonic way for doing that? :) Thanks! (crosspost from http://stackoverflow.com/questions/3119026/extension-modules-and-common-routines-in-python-c-api )
From: Stefan Behnel on 28 Jun 2010 03:30
ty ty, 28.06.2010 08:16: > I'm writing wrapper for C library. This library consist of several > parts. And i want split my extension package into different extension > modules. I think, this is the right way ;-) Depends. If it's somewhat large or deals with sufficiently distinct functionality, it might be worth doing. > But, there are some common > parts that exist in extension package, get_library_version, Error, and > so on. I've decided to create additional module, named core, where these > routines and variables are defined. Is that supposed to be used by Python code or internally by your modules? If it's the latter, I'd just write a plain C module and link it into each of the extension modules that use it. Otherwise, a common utility module might be ok, but I don't know anything about your real code that would suggest either way. You may also consider taking both approaches, i.e. write a linked-in module and a public Python wrapper around it. > And when get_library_version, for > example, is used by programmer, Error, in opposite, is used by routines > in another modules. As i mentioned in ( above mail), i use create_error > for adding new exception class with neccessary fields. Now i call > create_error in initcore function, which initialize core module. But, if > i don't import package.core, and only import package.module, when > package.module.function fails , python's runtime throws error Obviously. Just make sure you always import your core module first. If it defines something as basic as the main error class (assuming that's what you meant with "Error"), I'd make that the very first thing in the init function. You might also want to take a look at Cython. It's a Python dialect that makes writing extension modules easy, so if you have a lot of C code to wrap, it'll help you get it done substantially faster than in plain C code. Stefan |