Block os import and any other system import in python

block_system_import.py

from contextlib import contextmanager
@contextmanager
def block_system_import():
    block_import = ["os",'sys']
    saved = {}
    import sys
    for i in block_import:
        saved[i] = sys.modules[i]
        sys.modules[i] = None
    yield None
    for i in block_import:
        sys.modules[i] = saved[i]

with block_system_import():
    try:
        import sys
    except ModuleNotFoundError:
        print("Success could not import modules inside context manager")

import sys
import os

print("Import sys packages outside context manager succeeded")