[issue41878] python3 fails to use custom mapping object as symbols in eval()

[Josh Rosenberg]

Change by Josh Rosenberg :


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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue41878] python3 fails to use custom mapping object as symbols in eval()

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Robert, this tracker is for patching CPython, not for debugging user code.  If, 
as it appears, you are not suggesting the former, please close this.  For the 
latter, python-list and stackoverflow.com are appropriate forums.

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nosy: +terry.reedy

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[issue41878] python3 fails to use custom mapping object as symbols in eval()

[Robert Haschke]

Robert Haschke  added the comment:

Thanks, Josh, for this clarification. What is the suggested mitigation?
Obviously, I need to pass all symbols from my hierarchical dictionary in a 
flattend version as a dict to globals. Or do you see another option?

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[issue41878] python3 fails to use custom mapping object as symbols in eval()

[Josh Rosenberg]

Josh Rosenberg  added the comment:

Yes, list comprehensions having their own local scope was a change from Py2 to 
Py3. Python 2 did not do this for list comps initially, and it was left that 
way during the 2.x timeframe due to back compat constraints, but 2.x did it 
from the start for generator expressions, as well set and dict comps, and they 
were all made consistent for Py3.

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nosy: +josh.r

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[issue41878] python3 fails to use custom mapping object as symbols in eval()

[Robert Haschke]

Robert Haschke  added the comment:

Looks like the list generator is considered as a new nested scope, which 
prohibits access to local variables?
This basic expression, passing local symbols only, fails as well:

eval('[abc[i]*abc[i] for i in [0, 1, 2]]', {}, dict(abc=[1, 2, 3]))

while this one, passing dict as global symbols, works:

eval('[abc[i]*abc[i] for i in [0, 1, 2]]', dict(abc=[1, 2, 3]))

However, passing globals must be a real dict. So I cannot simply pass my custom 
mapping to globals.

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title: python3 fails to use custom dict-like object as symbols in eval() -> 
python3 fails to use custom mapping object as symbols in eval()

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