input: Write a function named `create_basic_blockchain` that creates and returns an instance of a basic blockchain using only the core modules in Python. The function should import necessary modules and define the Blockchain class with methods to create a block, get the current timestamp, and hash a block. The function should return the instantiated Blockchain object.
  
  assert isinstance(create_basic_blockchain(), Blockchain)==True
  blockchain = create_basic_blockchain()
  assert blockchain.create_block(0, '0')['block_number']==1
  assert len(blockchain.chain)==1
  assert blockchain.hash_block(blockchain.chain[0]).startswith('0')==True
output: import hashlib
  import time
  
  class Blockchain:
      def __init__(self):
          self.chain = []
          self.create_block(1, '0')
  
      def create_block(self, proof, previous_hash):
          block = {
              'block_number': len(self.chain) + 1,
              'timestamp': self.get_current_timestamp(),
              'proof': proof,
              'previous_hash': previous_hash
          }
          self.chain.append(block)
          return block
  
      def get_current_timestamp(self):
          return time.time()
  
      def hash_block(self, block):
          block_string = str(block).encode()
          return hashlib.sha256(block_string).hexdigest()
  
  def create_basic_blockchain():
      return Blockchain()