On the ESP8266, because it’s all in Python, the code is similar. In fact, the same basic code would work between two computers running vanilla Python just as well as the ESP8266 running MicroPython.

[Damien] sent us a quick email to let us know that Micro Python, a lean and fast implementation of the Python scripting language on microcontrollers is now running on the ESP8266. You may remember … ...

The only time to pickle something is if you need to represent a non-string object on disk, but Python code is strings. I presume that the receiving program is basically calling eval (skt.recv ()).