human
Solve the following python programming problem given the following code:
@ feature ('tarball') 
def feature_tarball(tgen) : 
    '
    Handle a tarball source.  Implements steps seturl, download and unpack
    ' 
    tgen.step ('seturl', rule = ("echo '%s' > %s" % (tgen.worch.source_url, tgen.worch.source_urlfile)), update_outputs = True, target = tgen.worch.source_urlfile) 
    def dl_task(task) : 
        src = task.inputs [0] 
        tgt = task.outputs [0] 
        url = src.read ().strip () 
        try : 
            web = urlopen (url) 
            tgt.write (web.read (), 'wb') 
except Exception : 
            import traceback 
            traceback.print_exc () 
            msg.error (tgen.worch.format ('[{package}_download] problem downloading [{source_url}]')) 
            raise 
checksum = tgen.worch.source_archive_checksum 
        if (not checksum) : 
            return 
(hasher_name, ref) = checksum.split (':') 
        import hashlib, os 
        hasher = getattr (hashlib, hasher_name) () 
        hasher.update (tgt.read ('rb')) 
        data = hasher.hexdigest () 
        if (data != ref) : 
            msg.error (tgen.worch.format (('[{package}_download] invalid checksum:
ref: %s
new: %s' % (ref, data)))) 
            try : 
                os.remove (tgt.abspath ()) 
except IOError : 
                pass 
return 1 
return 
tgen.step ('download', rule = dl_task, source = tgen.worch.source_urlfile, target = tgen.worch.source_archive_path) 
    def unpack_task(task) : 
        cmd = get_unpacker (task.inputs [0].abspath ()) 
        return exec_command (task, cmd) 
tgen.step ('unpack', rule = unpack_task, source = tgen.worch.source_archive_path, target = unpack_task.worch.source_unpacked_target) 
    return 

    
    

    Fix the buggy line: tgen.step ('unpack', rule = unpack_task, source = tgen.worch.source_archive_path, target = unpack_task.worch.source_unpacked_target)
assistant
#Here is Python program to fix the buggy line: tgen.

tgen.step ('unpack', rule = unpack_task, source = tgen.worch.source_archive_path, target = tgen.worch.source_unpacked_target)