I'd like advice/opinions on when it is appropriate to do
attribute/property validation in python. I'm coming from a C#/Java
background, where of course tons of "wasted" code is devoted to
property validation. Here is a toy example illustrating my question:
# Example: mixing instance attributes with properties. Is it pythonic to
# validate property data in setters? Since tens and ones are never
# validated, the class can be "broken" by setting these directly
class SillyDecimal(object):
"""A silly class to represent an integer from 0 - 99."""
def __init__(self, arg=17):
if isinstance(arg, tuple):
self.tens = arg[0]
self.ones = arg[1]
else:
self.number = arg
def getNumber(self):
return self.tens*10 + self.ones
def setNumber(self, value):
if value < 0 or value > 99:
raise ArgumentException("Must in [0, 99]")
self.tens = value // 10
self.ones = value % 10
number = property(getNumber, setNumber, None, "Complete number, [0-99]")
x = SillyDecimal()
x.number, x.tens, x.ones # returns (17, 7, 1)
Even though "tens", "ones" and "number" all appear as attributes, only
"number" has its input validated. Since the class is designed to only
hold numbers 0 - 99, one can 'break' it by setting self.tens=11, for
example. Should tens and ones be made into full-fledged properties
and validated? Should number have no validation? Is it more pythonic
to encapsulate tightly, or rely on "responsible use."
Marcus
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