input: Write a function to implement a simple hash table with put and get methods.
  assert hash_table.put('banana', 'yellow') is None
  assert hash_table.get('banana') == 'yellow'
  assert hash_table.put('grape', 'purple') is None
  assert hash_table.get('grape') == 'purple'
  assert hash_table.put('apple', 'green') is None
  assert hash_table.get('apple') == 'green'
output: class SimpleHashTable:
      def __init__(self):
          self.table = {}
      
      def put(self, key, value):
          self.table[key] = value
      
      def get(self, key):
          return self.table.get(key, None)
  
  hash_table = SimpleHashTable()