Use module defined constants in pythoncode block

Question

My C code defines a constant, I'm trying to add python code (in a pythoncode block) that uses that constant, for some reason this doesn't work.

Demonstration .i file:

%module test
%{
// c code defines a static constant
static const int i=3;
%}

// declare the constant so that it shows up in the python module
static const int i;

%pythoncode %{
# try to use the constant in some python code
lookup={'i':i,}
%}

Here's the error:

[dave]$ python -c "import test"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "test.py", line 70, in <module>
    lookup={'i':i,}
NameError: name 'i' is not defined

If I comment out the lookup dictionary in the pythoncode block, everything works fine:

[dave]$ python -c "import test; print test.i"
3

so at least when I import the module the constant shows up.

How can I "see" the C-defined constants in my pythoncode block?

swig 2.0.4, python 2.7.

tynn · Accepted Answer · 2015-07-10 19:10:47Z

2

Adding additional Python code states for %pythoncode:

This code gets inserted in to the .py file created by SWIG.

So let's tail the generated test.py:

# try to use the constant in some python code
lookup={'i':i,}

# This file is compatible with both classic and new-style classes.

cvar = _test.cvar
i = cvar.i

The %pythoncode was inserted before i is defined. Since it's the first and only appearance, you might need to use _test.cvar.i directly instead:

%pythoncode %{
# try to use the constant in some python code
lookup={'i': _test.cvar.i,}
%}

answered Jul 10, 2015 at 19:10

tynn

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Dave · Accepted Answer · 2015-07-10 19:36:36Z

1

Another workaround is to defer referencing the variable until after the module completes loading, by using a function:

%pythoncode %{
def lookup( key ){
     mp={'i':i}
     return mp[key]
%}

answered Jul 10, 2015 at 19:36

Dave

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