I've got a structure defined inside header.h that looks like :
typedef struct {
....
int icntl[40];
double cntl[15];
int *irn, *jcn;
....
When I init an object with this structure, I have access to integers/doubles but not arrays.
>> st.icntl
<Swig Object of type 'int *' at 0x103ce37e0>
>> st.icntl[0]
Traceback (most recent call last):
File "test_mumps.py", line 19, in <module>
print s.icntl[0]
TypeError: 'SwigPyObject' object is not subscriptable
How to have access to the values in read/write?
The easiest way to do this is to wrap your arrays inside a struct
, which can then provide extra methods to meet the "subscriptable" requirements.
I've put together a small example. It assumes you're using C++, but the equivalent C version is fairly trivial to construct from this, it just requires a bit of repetition.
First up, the C++ header that has the struct
we want to wrap and a template that we use for wrapping fixed size arrays:
template <typename Type, size_t N>
struct wrapped_array {
Type data[N];
};
typedef struct {
wrapped_array<int, 40> icntl;
wrapped_array<double, 15> cntl;
int *irn, *jcn;
} Test;
Our corresponding SWIG interface then looks something like:
%module test
%{
#include "test.h"
#include <exception>
%}
%include "test.h"
%include "std_except.i"
%extend wrapped_array {
inline size_t __len__() const { return N; }
inline const Type& __getitem__(size_t i) const throw(std::out_of_range) {
if (i >= N || i < 0)
throw std::out_of_range("out of bounds access");
return self->data[i];
}
inline void __setitem__(size_t i, const Type& v) throw(std::out_of_range) {
if (i >= N || i < 0)
throw std::out_of_range("out of bounds access");
self->data[i] = v;
}
}
%template (intArray40) wrapped_array<int, 40>;
%template (doubleArray15) wrapped_array<double, 15>;
The trick there is that we've used %extend
to supply __getitem__
which is what Python uses for subscript reads and __setitem__
for the writes. (We could also have supplied a __iter__
to make the type iteratable). We also gave the specific wraped_array
s we want to use unique names to make SWIG wrap them in the output.
With the supplied interface we can now do:
>>> import test
>>> foo = test.Test()
>>> foo.icntl[30] = -654321
>>> print foo.icntl[30]
-654321
>>> print foo.icntl[40]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "test.py", line 108, in __getitem__
def __getitem__(self, *args): return _test.intArray40___getitem__(self, *args)
IndexError: out of bounds access
You might also find this approach useful/interesting as an alternative.
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