[New-bugs-announce] [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:

<class 'decimal.Decimal'> <class 'decimal.Decimal'> False <class '__main__.MyDecimal'> 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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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16431>
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