Version:
Python 3.10.0 - Windows 11 (22000.258) x64
Python 3.9.7 - Windows 11, Manjaro Linux 21.1.5 - Kernel 5.13.13-1-MANJARO x64
CPU: 8 × Intel® Core™ i5-8300H CPU @ 2.30GHz

Steps to reproduce:
1. Create any list, for example your_list = [1, 2, 3]
2. Execute [your_list.append(i) for i in your_list]

This is intentional behaviour, you actually created an infinite loop. When you iterate over a list, all Python does is track the current index through the list internally, incrementing it each time. But each iteration, you call list.append() to add a new item to the end of the list, so you're continually making it longer and preventing the iteration from ending.

Regardless of that, this probably isn't a good use of list comprehensions anyway - append() always returns None, so the result of this comprehension would be a useless list of Nones. It'd be better to just use a regular for loop, or if you're just wanting to copy the list call list.copy() or list(your_list).

It is expected behavior. Your code is equivalent to:

_result = []
for i in your_list:
    _result.append(your_list.append(i))

which is equivalent to:

_result = []
_j = 0
while _j < len(your_list):
    i = your_list[_j]
    _result.append(your_list.append(i))
    _j += 1

It is an infinite loop (because len(your_list) is increased after your_list.append(i)), and two lists grow with every iteration.