[FIXED] My asynchronous decorator keeps on returning a NoneType error

Issue

I'm trying to code a socket server on my raspberry pi. I'm trying to use a decorator to connect a client to a server(which will be my raspberry pi). But my code for it is keeping on throwing a NoneType error. I'm a bit new to asynchronous decorators, and need some help on them. Can you please see where my error is coming from, and please correct my code a bit? I will list my code and the error messages down below.

My error message:

C:\Users\####\AppData\Local\Programs\Python\Python36-32\python.exe C:/Users/#####/Desktop/autorank/server/client.py
Traceback (most recent call last):
  File "C:/Users/#####/Desktop/autorank/server/client.py", line 5, in <module>
    @client.connection(("192.168.0.11", 56500))
TypeError: 'NoneType' object is not callable

My client code for the package:

import socket, asyncio

class Client:
    def __init__(self):
        self.s = None
        self.data = None

    def connection(self, addr):
        """An asynchronous decorator for any server mainloop. Just decorate it with this and add a Client parameter."""

        def wrapper1(func):
            async def wrapper2(*args):
                self.connect(addr)
                await func(self)
                self.close_conn()
                return await func(self)
            return wrapper2

    async def connect(self, addr):
        """Connects to the desired server. You can make a server mainloop with the connection decorator."""

        self.s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.s.connect(addr)

        self.addr = addr

        print(f"Connected to {addr}")

    async def close_conn(self):
        """Closes connection with the address connected to."""

        self.s.close()

        print(f"Disconnected from {self.addr}")
        del self.addr

    async def send_bytes(self, bytes_data):
        """Sends bytedata through a pipe to connected address"""

        self.s.sendall(bytes_data)

        print(f"Sent {bytes_data.decode()} in bytedata format to {self.addr}")

    async def recv(self, buf_size):
        """Recieves data from a server in bytedata format"""

        self.data = self.s.recv(buf_size)

And finally, my main.py:

import asyncserver

client = asyncserver.Client()

@client.connection(("192.168.0.11", 56500))
def mainloop(cli):
    cli.send_bytes(b'Hello!!')
    cli.recv(1024)
    print(cli.data.decode())

Please say if I should improve my question, and any answers are appreciated!

Solution

The connection decorator correctly defines wrapper1, but fails to return it. It implicitly returns None, and that's what gets used as mainloop at top-level, resulting in the error.

Note that wrapper2 awaits func(self), which might lead to another error, about None not being awaitable. If you plan to await the function you decorate, you should either make it async (async def mainloop(cli): ...) or have it return an awaitable object.

Finally, wrapper2 shouldn't accept arbitrary *args if it will not use them. That will cause something like mainloop(1, 2, 3) to appear to work while ignoring the arguments. Normally the point of a wrapper accepting *args is to forward them to the wrapped function. If you don't want or need that, just make the wrapper2 accept no arguments.

Answered By - user4815162342