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Jason Baker, 31.05.2010 22:31:
On Mon, May 31, 2010 at 3:06 PM, Stefan Behnel wrote:
Jason Baker, 31.05.2010 21:45:
On Mon, May 31, 2010 at 2:05 PM, Stefan Behnel wrote:
Jason Baker, 31.05.2010 18:15:
I'm looking for a way to convert Python objects into Scheme values. Essentially what I'm trying to do is say "Is this a Python integer? Ok, convert it to a Scheme integer." or "Is this a Python string? Ok, convert it into a Scheme string." ... etc.
What is the best way to do this? My first intuition was to call Py*_Check to determine the type, but it turns out that's a macro that can't be used in non-c code. I'm sure I could translate that into the appropriate C code, but that gives me a bad feeling.
Those are macros because that makes them really, really fast, especially in Py3. However, their definition changes between Python versions, so replacing them by regular C code is really not a good idea.
In general, I wouldn't try to make the wrapper too generic. You might want to inspect the underlying Scheme code (potentially at runtime), and infer the possible types (or the required conversion) from that.
Perhaps I should clarify. For now, I'm just trying to embed the python interpreter in Scheme. Thus, I know what types the scheme values are, and I know how to translate them into the appropriate Python values. What I'm trying to figure out is how to go the other way. That is, how do I figure out what type a PyObject is so I know how to create the appropriate Scheme value?
Why not write a type checking cascade in plain C or Cython?
I suppose I could, but I'd rather write it in pure Scheme or Python if at all possible. If that's not efficient enough, I can look into adding C into the mix.
You could build a dict that maps any combination of a builtin Python type and a Scheme type to a way to convert the first to the second. That might even be faster than a type checking cascade in C. Structured types would fall back to the standard Python type conversion rules.