builtin discovery #37
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added 2 commits
October 15, 2019 13:31
According the CPython, the parent's builtins are only selected if the `f_globals` of the parent are exactly the same as the `f_globals` of the function to be executed. If not, the builtins are read from the `__builtins__` of the current function's `f_globals`, not the `f_locals`. https://github.com/python/cpython/blob/3cd21aa6a1467723ccc85e6411a6cbe7fa81ef76/Objects/frameobject.c#L624-L654
When a frame's globals differ from it's parents, or a frame is the top of the
execution stack, but there is no `__builtins__`, then the builtins should just
be {'None': None}.
https://github.com/python/cpython/blob/3cd21aa6a1467723ccc85e6411a6cbe7fa81ef76/Objects/frameobject.c#L636-L643
gerrymanoim
reviewed
Oct 16, 2019
| def f(NameError=NameError, AssertionError=AssertionError): | ||
| # capture NameError and AssertionError early because | ||
| # we are deleting the builtins | ||
| None |
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Is the None here just a test that the builtins are now {'None': None}
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I should add a comment here. The default builtins, when not inherited nor provided in the globals, is just the mapping {'None': None}. Having this name lookup here was supposed to test that the name None resolves to None. I believe this test is insufficient in Python 3 where None will compile into a LOAD_CONST instead of a LOAD_GLOBAL or LOAD_NAME. I am not totally sure how to test that None is actually in the builtins given that by definition of this test, there is no __builtins__ object in scope.
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One small understanding question, but otherwise LGTM. |
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Fixes two issues in the way the builtins get found for a frame:
f_back.f_globals is f_globals.__builtins__is undefined in thef_globals, then the builtins are a new dictionary with a value of{'None': None}.References to the CPython source are provided in the two commit messages.