I have an input file data, a python function parse and a template. What I am trying to do is use parse function to get dictionary out of data and use that to replace fields in template.

Now to make this a bit more generic (I perform the same action in few places) I have defined a custom function to do so. Below is definition of custom builder and values is a dictionary with { 'name': (data_file, parse_function) } (you don't really need to read through this, I simply put it here for completeness).

def TOOL_ADD_FILL_TEMPLATE(env):
    def FillTemplate(env, output, template, values):
        out = output[0]

        subs = {}
        for name, (node, process) in values.iteritems():
            def Process(env, target, source):
                with open( env.GetBuildPath(target[0]), 'w') as out:
                    out.write( process( source[0] ) )

            builder = env.Builder( action = Process )
            subs[name] = builder( env, env.GetBuildPath(output[0])+'_'+name+'_processed.cpp', node )[0]

        def Fill(env, target, source):
            values = dict( (name, n.get_contents()) for name, n in subs.iteritems() )
            contents = template[0].get_contents().format( **values )
            open( env.GetBuildPath(target[0]), 'w').write( contents )

        builder = env.Builder( action = Fill  )
        builder( env, output[0], template + subs.values() )

        return output

    env.Append(BUILDERS = {'FillTemplate': FillTemplate})

It works fine when it comes to checking if data or template changed. If it did it rebuilds the output. It even works if I edit process function directly. However if my process function looks like this:

def process( node ):
    return subprocess(node)

and I edit subprocess the change goes unnoticed. Is there any way to get correct builds without making process functions being always invoked?