<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _structure(self, source_code):
 """return structure in ACDP format."""

        # define cutter as a per block reader
        def cutter(seq, block_size):
            for index in range(0, len(seq), block_size):
                lexem = seq[index:index+block_size]
                if len(lexem) == block_size:
                    yield self.table_struct[seq[index:index+block_size]]
        return tuple(cutter(source_code, self.idnt_struct_size))