input: Write a function to create a basic blockchain in Python using only core modules. The function should initialize a Blockchain object, create a block with a given nonce and previous hash, and return the created block. The function should also include a method to return the current timestamp and a method to hash a given block using the SHA-256 algorithm.
  
  def create_blockchain_block(nonce, previous_hash):
   import hashlib
   import json
   import time
  
   class Blockchain:
    def __init__(self):
     self.chain = []
     self.transactions = []
  
    def create_block(self, nonce, previous_hash):
     block = {
      'block_number': len(self.chain) + 1,
      'timestamp': self._current_timestamp(),
      'nonce': nonce,
      'previous_hash': previous_hash
     }
     self.chain.append(block)
     return block
  
    def _current_timestamp(self):
     return round(time.time() * 1000)
  
    def hash_block(self, block):
     string_object = json.dumps(block, sort_keys=True)
     block_string = string_object.encode()
     raw_hash = hashlib.sha256(block_string)
     hex_hash = raw_hash.hexdigest()
     return hex_hash
  
   blockchain = Blockchain()
   return blockchain.create_block(nonce, previous_hash)
  
  assert create_blockchain_block(12345, '0')['block_number'] == 1
  assert create_blockchain_block(67890, '0')['nonce'] == 67890
  assert create_blockchain_block(12345, '0')['previous_hash'] == '0'
  assert create_blockchain_block(12345, '0')['block_number'] == 1
  assert isinstance(create_blockchain_block(12345, '0'), dict)
output: def create_blockchain_block(nonce, previous_hash):
   import hashlib
   import json
   import time
  
   class Blockchain:
    def __init__(self):
     self.chain = []
     self.transactions = []
  
    def create_block(self, nonce, previous_hash):
     block = {
      'block_number': len(self.chain) + 1,
      'timestamp': self._current_timestamp(),
      'nonce': nonce,
      'previous_hash': previous_hash
     }
     self.chain.append(block)
     return block
  
    def _current_timestamp(self):
     return round(time.time() * 1000)
  
    def hash_block(self, block):
     string_object = json.dumps(block, sort_keys=True)
     block_string = string_object.encode()
     raw_hash = hashlib.sha256(block_string)
     hex_hash = raw_hash.hexdigest()
     return hex_hash
  
   blockchain = Blockchain()
   return blockchain.create_block(nonce, previous_hash)