Don't do it. Really, really don't do it. People have tried for decades to develop such a sandbox, and it does not work.
for me I just want to hijack the interpreter so I don't have to write my own. no imports, no sockets.
I'm talking about the history beyond why rexec and Bastion, and restricted execution, were removed from Python in the 2.x days. See https://python.readthedocs.io/en/v2.7.2/library/restricted.h... , "In Python 2.3 these modules have been disabled due to various known and not readily fixable security holes."
They started because back in the 1.x days there was a Python web browser called Grail, and the hope was to support restricted Python applets in Grail.
Or from 10 years ago, read https://lwn.net/Articles/574215/ about the failure of 'pysandbox' where one of the ways to break out was to "[use] a traceback object to unwind the stack frame to one in the trusted namespace, then use the f_globals attribute to retrieve a global object." ... "Stinner's tale should serve as a cautionary one to anyone considering a CPython-based solution".
You might consider RestrictedPython at https://restrictedpython.readthedocs.io/en/latest/ which supports only a subset of Python, via AST-walking to limit what the code can do. I have no experience with it.
edit: here are my silly little patches: https://github.com/hananbeer/cpython-toy-sandbox/commit/fa3f...
this is of course assuming exec(globals={..}) without certain builtins and is, again, not expected to use system apis like files or sockets or anything.
d = {"__builtins__": {"print": print}}
exec("""
def delay_until_gc():
try:
try:
yield 1
finally:
print((1).__class__.__bases__[0].__subclasses__()[:3])
except:
raise
it = delay_until_gc()
it.__next__()
""", d, d)
del d
print("Finished exec.")
Finished exec.
[<class 'type'>, <class 'async_generator'>, <class 'bytearray_iterator'>]
import gc
toybox(1)
exec(..., d, d)
del d
gc.collect()
toybox(0)
If you allow any mutable object into the globals or locals dictionary, such that the exec'ed code can attach something to it, then you can't even use gc.collect() to ensure the exec'ed code can no longer be executed.