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context manager methods (__enter__ and __exit__) raise a SyntaxError #230
Description
BUG/PROBLEM REPORT (OR OTHER COMMON ISSUE)
If this ticket is accepted as a bug or feature request, I volunteer to work on it (once contributor agreement is approved).
What I did:
I tried to create a context manager in restricted python, here is the code:
from RestrictedPython import compile_restricted
source_code = """
class example:
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, exc_traceback):
pass
"""
compile_restricted(source_code, '<inline>', 'exec')
What I expect to happen:
I expected to have a context manager that I could use in a with statement
What actually happened:
I get the following error:
SyntaxError: ('Line 3: "__enter__" is an invalid variable name because it starts with "_"', 'Line 6: "__exit__" is an invalid variable name because it starts with "_"')
These methods (__enter__ and __exit__) are missing from transformer.ALLOWED_FUNC_NAMES
What version of Python and Zope/Addons I am using:
Python 3.8.2
RestrictedPython 5.2
macOS Monterey 12.5.1
Activity
icemac commentedon Aug 24, 2022
Currently you are not able to define a context manager inside restricted Python because the needed method names start with
_.But I see the value in being able to do so.
A pull request is welcome adding
__enter__and__exit__toALLOWED_FUNC_NAMESincluding a test showing that context managers can be defined and used afterwards in restricted Python.icemac commentedon Sep 30, 2026
I changed my mind about this one. See #333 for the details.
Allowing
__exit__would give restricted code the traceback object. Through it, restricted code could reach the frames of trusted code, which it cannot reach today. I think that risk is too big.Nothing is lost by not allowing context managers to be defined in restricted code: they are syntactic sugar for
try/finally, which restricted code can already use. Context managers provided by trusted code already work inwithstatements.Closing as "won't fix".