jb****@rubic.com wrote:
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)
