smtpd.PureProxy(localaddr="host1", remoteaddr="host2")

...produces the error:

[...] smtpd.py", line 657, in __init__
    gai_results = socket.getaddrinfo(*localaddr, type=socket.SOCK_STREAM)
TypeError: getaddrinfo() got multiple values for argument 'type'

The module only works with:

smtpd.PureProxy(localaddr=("host1", 25), remoteaddr=("host2", 25))

The documentation does not specify the format of the INPUT parameters, only the CLI syntax with hostnames as "host:port" strings.
The underlying library should convert them to tuples or at least the documentation should be completed.