[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Stefan Krah]

Stefan Krah added the comment:

Thanks, Amaury. Should be fixed now.

--
resolution:  -> fixed
stage:  -> committed/rejected
status: open -> closed

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Roundup Robot]

Roundup Robot added the comment:

New changeset 9a701e8ec2c9 by Stefan Krah in branch '3.3':
Issue #16431: Finally, consider all permutations.
http://hg.python.org/cpython/rev/9a701e8ec2c9

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

"Py_INCREF(v); return v;" should be used only for immutable types, not for 
subclasses. in 3.2, the code below prints "3, None":

import decimal
class MyDecimal(decimal.Decimal):
x = None
def __new__(cls, value):
return super().__new__(cls, value)
return obj
a = MyDecimal("1.1")
a.x = 3
b = MyDecimal(a)
print(a.x, b.x)

--
nosy: +amaury.forgeotdarc

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Roundup Robot]

Roundup Robot added the comment:

New changeset 7fcc58811e82 by Stefan Krah in branch '3.3':
Issue #16431: Also fix the opposite direction.
http://hg.python.org/cpython/rev/7fcc58811e82

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Roundup Robot]

Roundup Robot added the comment:

New changeset 1b6c972457e6 by Stefan Krah in branch '3.3':
Issue #16431: Use the type information when constructing a Decimal subtype
http://hg.python.org/cpython/rev/1b6c972457e6

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nosy: +python-dev

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Yury Selivanov]

Changes by Yury Selivanov :


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nosy: +yselivanov

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Mark Dickinson]

Changes by Mark Dickinson :


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nosy: +mark.dickinson

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[issue16431] CDecimal disregards subclass passed into __new__ when value argument is an instance of Decimal

[Elvis Pranskevichus]

New submission from Elvis Pranskevichus:

Consider the following:

import decimal

class MyDecimal(decimal.Decimal):
def __new__(cls, value):
return super().__new__(cls, value)

a = decimal.Decimal('1.0')
b = MyDecimal(a)
c = MyDecimal('1.0')

print(type(a), type(b), isinstance(b, MyDecimal), type(c), isinstance(c, 
MyDecimal))

Running the above in 3.3 produces:

  False  True

Which shows that Decimal.__new__(cls, Decimal()) will always return its 
argument regardless of cls.

--
messages: 175121
nosy: Elvis.Pranskevichus, skrah
priority: normal
severity: normal
status: open
title: CDecimal disregards subclass passed into __new__ when value argument is 
an instance of Decimal
type: behavior
versions: Python 3.3, Python 3.4

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