redis.exceptions.ConnectionError: Error 111 connecting to localhost:6379. Connection refused.

$ pip install redis
>>> import redis
>>> conn = redis.Redis()
>>> conn.keys('*')
Traceback (most recent call last):
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 484, in connect
sock = self._connect()
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 541, in _connect
raise err
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 529, in _connect
sock.connect(socket_address)
ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/henry/.local/lib/python3.5/site-packages/redis/client.py", line 667, in execute_command
connection.send_command(*args)
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 610, in send_command
self.send_packed_command(self.pack_command(*args))
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 585, in send_packed_command
self.connect()
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 489, in connect
raise ConnectionError(self._error_message(e))
redis.exceptions.ConnectionError: Error 111 connecting to localhost:6379. Connection refused.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 484, in connect
sock = self._connect()
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 541, in _connect
raise err
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 529, in _connect
sock.connect(socket_address)
ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/henry/.local/lib/python3.5/site-packages/redis/client.py", line 1032, in keys
return self.execute_command('KEYS', pattern)
File "/home/henry/.local/lib/python3.5/site-packages/redis/client.py", line 673, in execute_command
connection.send_command(*args)
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 610, in send_command
self.send_packed_command(self.pack_command(*args))
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 585, in send_packed_command
self.connect()
File "/home/henry/.local/lib/python3.5/site-packages/redis/connection.py", line 489, in connect
raise ConnectionError(self._error_message(e))
redis.exceptions.ConnectionError: Error 111 connecting to localhost:6379. Connection refused.
上面是错误代码，出现这样的错误，解决方案：

这个问题是因为没安装Redis服务器造成的。 

要么是安装一个redis，或者是启动redis。