input: Write a function to create a basic blockchain in Python using only the core modules. If successful, return the instance of the Blockchain class. If any error occurs, return None.
  assert create_blockchain() != None
  assert isinstance(create_blockchain(), Blockchain) 
  assert create_blockchain().chain == []
output: def create_blockchain():
      try:
          class Block:
              def __init__(self, index, previous_hash, timestamp, data, hash):
                  self.index = index
                  self.previous_hash = previous_hash
                  self.timestamp = timestamp
                  self.data = data
                  self.hash = hash
  
          class Blockchain:
              def __init__(self):
                  self.chain = []
  
          return Blockchain()
      except:
          return None