I was interested in playing around with Decimal and subclassing it. For example, if I wanted a special class to permit floats to be automatically converted to strings.
from decimal import Decimal
class MyDecimal(Decimal): def __init__(self, value): if isinstance(value, float): ... initialize using str(float) ...
In the classic days, I would have added something like this to MyDecimal __init__:
Decimal.__init__(self, str(value))
But I'm unfamiliar with the __new__ protocol.
__new__ is called to create a new instance of the class. It is a staticmethod that gets passed as its first parameter the class to be created. You should be able to do something like[1]:
py> import decimal
py> class MyDecimal(decimal.Decimal):
... def __new__(cls, value):
... if isinstance(value, float):
... value = str(value)
... return super(MyDecimal, cls).__new__(cls, value)
...
py> MyDecimal(3.0)
Decimal("3.0")STeVe
[1] If you're really afraid of super for some reason, you can replace the line:
return super(MyDecimal, cls).__new__(cls, value)
with
return decimal.Decimal.__new__(cls, value)
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