<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _BuildDelete(self, subject, attribute=None, timestamp=None):
 """Build the DELETE query to be executed."""

    subjects_q = {
        "query": "DELETE subjects FROM subjects WHERE hash=unhex(md5(%s))",
        "args": [subject]
    }

    aff4_q = {
        "query": "DELETE aff4 FROM aff4 WHERE subject_hash=unhex(md5(%s))",
        "args": [subject]
    }

    locks_q = {
        "query": "DELETE locks FROM locks WHERE subject_hash=unhex(md5(%s))",
        "args": [subject]
    }

    if attribute:
      aff4_q["query"] += " AND attribute_hash=unhex(md5(%s))"
      aff4_q["args"].append(attribute)

      if isinstance(timestamp, (tuple, list)):
        aff4_q["query"] += " AND aff4.timestamp >= %s AND aff4.timestamp <= %s"
        aff4_q["args"].append(int(timestamp[0]))
        aff4_q["args"].append(int(timestamp[1]))

      attributes_q = {
          "query": "DELETE attributes FROM attributes LEFT JOIN aff4 ON "
                   "aff4.attribute_hash=attributes.hash "
                   "WHERE attributes.hash=unhex(md5(%s)) "
                   "AND aff4.attribute_hash IS NULL",
          "args": [attribute]
      }
      # If only attribute is being deleted we will not check to clean up
      # subject and lock tables.
      return [aff4_q, attributes_q]
    # If a subject is being deleted we clean up the locks and subjects table
    # but assume it has attributes that are common to other subjects

    return [aff4_q, locks_q, subjects_q]