在学习twisted的过程中，遇到的第一个例子就出了点问题。

self.transport.write("Hello World!")

在运行的时候会抛出以下错误

File "/usr/local/lib/python3.7/site-packages/twisted/internet/selectreactor.py", line 149, in _doReadOrWrite
    why = getattr(selectable, method)()
  File "/usr/local/lib/python3.7/site-packages/twisted/internet/tcp.py", line 627, in doConnect
    self._connectDone()
  File "/usr/local/lib/python3.7/site-packages/twisted/internet/tcp.py", line 656, in _connectDone
    self.protocol.makeConnection(self)
  File "/usr/local/lib/python3.7/site-packages/twisted/internet/protocol.py", line 514, in makeConnection
    self.connectionMade()
  File "echoclient.py", line 8, in connectionMade
    self.transport.write("Hello World!")
  File "/usr/local/lib/python3.7/site-packages/twisted/internet/_newtls.py", line 191, in write
    FileDescriptor.write(self, bytes)
  File "/usr/local/lib/python3.7/site-packages/twisted/internet/abstract.py", line 349, in write
    raise TypeError("Data must not be unicode")
builtins.TypeError: Data must not be unicode

解决办法就是把string类型的字符串，转为字节类型的字符串

"Hello World!".encode('utf-8')
或者
b"Hello world!"