On 23/02/13 10:50, neubyr wrote:
I would like to validate data attributes before the object is instantiated
or any changes thereafter. For example, following is a simple Person class
with name and age attributes. I would like to validate whether age is an
integer before it is added/changed in the object's dictionary. I have taken
a simple integer validation example, but it could be something like
DateField validation or X509 certificate validation as well. Following is
my example code:
class Person(object):
def __init__(self,name,age):
self.name = name
self.age = age
def get_age(self):
return self._age
def set_age(self,val):
try:
int(val)
self._age = val
except ValueError:
raise Exception('Invalid value for age')
The setter is unnecessarily complicated. Just let the ValueError, or TypeError,
or any other error, propagate:
def set_age(self,val):
self._age = int(val)
This will allow the user to pass ages as strings, which I assume you want because that's
what your code above does. instance.age = "6" will set the age to the int 6. If
all you want to accept are ints, and nothing else:
def set_age(self,val):
if isinstance(val, int):
self._age = val
else:
raise TypeError('expected an int, but got %r' % val)
def del_age(self):
del self._age
age = property(get_age,set_age,del_age)
In general, you would leave out the property deleter. I find that in general if
you're validating attributes, you want them to be present and valid, so
deleting should be an error.
--
Steven
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