Why does RestrictedPython behave differently when used with Python 3.6?

Question

I'm trying to use RestrictedPython (see documentation ) with Python 3.6 . The following code yields different results in Python 2.7 and in 3.6 :

from RestrictedPython import compile_restricted
from RestrictedPython.Guards import safe_builtins
restricted_globals = dict(__builtins__ = safe_builtins)

src = '''
open('/etc/passwd')
'''

code = compile_restricted(src, '<string>', 'exec')
exec(code) in restricted_globals

In Python 2.7 , the result is as expected:

Traceback (most recent call last):
  File "...Playground.py", line 10, in <module>
    exec(code) in restricted_globals
  File "<string>", line 2, in <module>
NameError: name 'open' is not defined

But in Python 3.6 , the results is:

Traceback (most recent call last):
  File "...Playground.py", line 10, in <module>
    exec(code) in restricted_globals
  File "<string>", line 2, in <module>
FileNotFoundError: [Errno 2] No such file or directory: '/etc/passwd'

The open name/method is now obviously known, which should not be the case. Why does this code behave different when used in 3.6 than when used in 2.7 ?

Answer 1

The way you should write your code for version 3.6 is presented here:

https://github.com/zopefoundation/RestrictedPython

Under "Problematic Code Example".

Namely, the following code will work, that is, open will be not defined:

from RestrictedPython import compile_restricted
from RestrictedPython import safe_builtins

source_code = """
open('/etc/passwd')
"""
byte_code = compile_restricted(source_code, '<inline>', 'exec')
exec(byte_code, {'__builtins__': safe_builtins}, {})

As for the reason why this happens, I don't have one, but I wanted to present a way of making it work anyways.