8000 decimal.getcontext() is not applied within bpython · Issue #918 · bpython/bpython · GitHub
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DorskFR opened this issue Sep 27, 2021 · 7 comments
Open

decimal.getcontext() is not applied within bpython #918

DorskFR opened this issue Sep 27, 2021 · 7 comments
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@DorskFR
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DorskFR commented Sep 27, 2021

Steps to reproduce:

bpython version 0.21 on top of Python 3.9.6
>>> import decimal
>>> decimal.getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow])
>>> decimal.getcontext().rounding = decimal.ROUND_HALF_UP 
>>> decimal.getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow])
>>>

expected the rounding to be changed.
also fails using setcontext()
@thomasballinger
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thomasballinger commented Sep 27, 2021 •
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Yikes, that's too bad. Apparently this is a "coroutine-local" thing? So guessing switching from greenlets to threads might not fix, instead it would take moving to async?

Maybe we should manually persist this between execution contexts? I want to learn more about coroutine-locals.

@thomasballinger
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This works in Python 3.6 and is broken in 3.7+.

@sebastinas
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Why wouldn't this work if we switch to threads? All the user code that is executed would be in exactly one thread.

@thomasballinger
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Maybe it will, I meant to say I don't know if it will or not because it's not a thread local, it's something else.

@sebastinas
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I'm not sure I can follow. The context is thread-local.

@thomasballinger
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thomasballinger commented Sep 27, 2021 •
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I don't really understand what a coroutine local is yet, but I think it's now sometimes (usually?) a coroutine-local instead based on the value of decimal.HAVE_CONTEXTVAR. Edit: reading more, it sounds like coroutine–locals (contexts) work with threads and additionally work with coroutines, so I think this distinction is not important here (unless we do something with coroutines).

@sebastinas sebastinas added the bug label Oct 12, 2021
@nicolaiarocci
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nicolaiarocci commented Jun 6, 2023 •
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Still needing help with Python 3.11.3. A workaround that might not apply to everyone is resorting to DefaultContext which works as expected:

bpython version 0.24 on top of Python 3.11.3
>>> import decimal
>>> decimal.getcontext().prec = 6
>>> decimal.Decimal(1) / decimal.Decimal(7)
Decimal('0.1428571428571428571428571429')

>>> decimal.DefaultContext.prec = 6
>>> decimal.Decimal(1) / decimal.Decimal(7)
Decimal('0.142857')

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@sebastinas @thomasballinger @nicolaiarocci @DorskFR
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