Problema con la ejecución del código web3.py

Estoy tratando de ejecutar este código

from web3 import Web3, HTTPProvider
import json
import pprint
import requests
from random import randint

# Debug flags
debug_transaction = False
debug_CALL_transactions = False

# Geth node parameters
rpcport = '4000'

# Experiment parameters
numBuckets = 50

# Instantiate web3
web3 = Web3(HTTPProvider('http://localhost:' + rpcport))
# Instantiate HTTP connection to Geth JSONRPC
session = requests.Session()

# Iterate over blocks and print transactions
latest = web3.eth.getBlock('latest').number

print (latest)

Pero sigo recibiendo este error.

Traceback (most recent call last):
  File "python", line 23, in <module>
  File "cytoolz/functoolz.pyx", line 232, in cytoolz.functoolz.curry.__call__
  File "cytoolz/functoolz.pyx", line 232, in cytoolz.functoolz.curry.__call__
  File "cytoolz/functoolz.pyx", line 232, in cytoolz.functoolz.curry.__call__
  File "cytoolz/functoolz.pyx", line 232, in cytoolz.functoolz.curry.__call__
  File "cytoolz/functoolz.pyx", line 232, in cytoolz.functoolz.curry.__call__
requests.exceptions.ConnectionError: HTTPConnectionPool(host='localhost', port=4000): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7fcaeb556f98>: Failed to establish a new connection: [Errno 111] Connection refused',))

Soy nuevo en todo esto. ¿Alguien puede decirme qué estoy haciendo mal? Estoy tratando de ejecutar el código en repl.it