input: 
  def HashTable:
      def __init__(self):
          self.table = [[] for _ in range(256)]
   
      def insert(self, key, value):
          h = hash(key) % 256
          for i, kv in enumerate(self.table[h]):
              if kv[0] == key:
                  self.table[h][i] = (key, value)
                  return
          self.table[h].append((key, value))
   
      def retrieve(self, key):
          h = hash(key) % 256
          for kv in self.table[h]:
              if kv[0] == key:
                  return kv[1]
   
      def delete(self, key):
          h = hash(key) % 256
          for i, kv in enumerate(self.table[h]):
              if kv[0] == key:
                  del self.table[h][i]
      """
      Implement a hash table in Python that supports insert, delete, and retrieve operations.
      >>> ht = HashTable()
      >>> ht.insert("key1", "value1")
      >>> ht.retrieve("key1")
      'value1'
      >>> ht.delete('key1')
      >>> ht.retrieve("key1")
      None
      """
  
output:     def __repr__(self):
          return str(self.table)