<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def fix_paths(self, paths):
 """ Fix the filenames in the iterable paths Returns: old2new: Mapping old_path --> new_path """

        old2new, fixed_exts = {}, []

        for path in list_strings(paths):
            newpath, ext = self._fix_path(path)

            if newpath is not None:
                #if ext not in fixed_exts:
                #    if ext == "1WF": continue
                #    raise ValueError("Unknown extension %s" % ext)
                #print(ext, path, fixed_exts)
                #if ext != '1WF':
                #    assert ext not in fixed_exts
                if ext not in fixed_exts:
                    if ext == "1WF": continue
                    raise ValueError("Unknown extension %s" % ext)
                fixed_exts.append(ext)
                old2new[path] = newpath

        return old2new