Pattern for error checking easiest-first?

[jquinn+google]

Heres the situation:

class AbstractThing() :
def changeMe(self,b lah):
if blah < 1:
raise MyException
self.blah = blah

class NetworkedThing( AbstractThing):
def changeMe(self,b lah):
if blah self.getUpperLi mitOverTheNetwo rkSlowly:
raise MyOtherExceptio n
AbstractThing.c hangeMe(self,bl ah)
The problem is that code like this does error checking backwards. A
call to NetworkedThing. changeMe will first do a slow error check and
then a fast one. Obviously there are various ways to get around this -
either have the subclass explicitly ask the superclass to error check
first, or vice totally versa. Is there some accepted pattern/idiom for
handling this issue?

[Gabriel Genellina]

On 20 ago, 18:01, jquinn+goo...@c s.oberlin.edu wrote:

The problem is that code like this does error checking backwards. A
call to NetworkedThing. changeMe will first do a slow error check and
then a fast one. Obviously there are various ways to get around this -
either have the subclass explicitly ask the superclass to error check
first, or vice totally versa. Is there some accepted pattern/idiom for
handling this issue?

What about this:

class AbstractThing() :
def changeMe(self,b lah):
self.verify_bla h(blah)
self.blah = blah

def verify_blah(sel f, blah):
if blah < 1:
raise MyException

class NetworkedThing( AbstractThing):
def verify_blah(sel f, blah):
AbstractThing.v erify_blah(blah )
if blah self.getUpperLi mitOverTheNetwo rkSlowly:
raise MyOtherExceptio n

That is, it's the verify step that is overriden/enhanced, not the
changeMe method that stays the same.

--
Gabriel Genellina