Consider the object_filenames method: def object_filenames (self, source_filenames, strip_dir=0, output_dir=''): if output_dir is None: output_dir = '' obj_names = [] for src_name in source_filenames: (base, ext) = os.path.splitext (src_name) if ext not in self.src_extensions: continue ^^^^^^^^^ Problem is here if strip_dir: base = os.path.basename (base) obj_names.append (os.path.join (output_dir, base + self.obj_extension)) return obj_names # object_filenames () If you specify a source-file with an unknown extension in the sources list, you later get a traceback later saying something like 'sources and targets must have the same length'. IMO we have two possibilities here: - assume that 'ext' is something which should be passed to the linker - raise an error like 'Don't know how to compile this file' Thomas Heller ION-TOF GmbH