Matt Wilson schrieb:
> On Feb 21, 6:48 pm, "Diez B. Roggisch" <[EMAIL PROTECTED]> wrote:
>
>> How about
>>
>> def f(self, a=[], b=[])
>>
>> Just a guess though. To be brutally honest I'm not sure if there even is
>> a validator invoked in case of no value being present at all. IF so,
>> you could of course create your own ForEach-validator that just does
>> this, overloading the _to_python-method (or whichever is needed, but I
>> guess that's the one) to return an empty list if the
>> super-implementation doesn't.
>
> I took a stab at making my own validator. Comments requested:
>
> class IntegerList(validators.FancyValidator):
> "Make sure that we get a list of integers back."
>
> messages = dict()
>
> def _to_python(self, value, state):
> if value == "empty list": return []
> elif isinstance(value, list): return [int(x) for x in value]
> else: return [int(value)]
>
> Then I changed my f controller to be like this:
>
> @validate(validators={'a':IntegerList()},
> 'b':IntegerList()})
> @expose()
> def f(self, a="empty list", b="empty list"):
> log.debug("a is %s." % a)
> log.debug("b is %s." % b)
> return dict(a=a, b=b)
>
> Everything seems to work OK.
>
> I don't like the idea of putting the empty lists into the method
> definition. I've had bad luck with that in the past when python would
> create a single list and keep it across function calls, like this:
Of course you need to be careful when using mutables as default
arguments. But your solution is worse - how do you distinguish between
"no argument passed" and "empty list" passed?
Usually, if one wants what you are after - getting a list in all
circumstances - the code then is supposed to look like this:
def foo(a):
for value in a:
...
without a preliminary check. In that case, you might as well use
def foo(a=()):
The empty tuple is immutable.
However, I'm a bit flabbergasted that the default-argument you pass to a
and b somewhow is really used in the validator. If that's the case, it
means that the validate-decorator somehow inspects the method signature.
Might that be as it is, IF things work that way, you are still better
off with a "None" there - which is also an immutable, and a much safer
value to use because it can't collide with a possible user-input. Think
of the same problem as yours, but without the int()-requirement. Then
entering "empty list" would be forbidden for your user.
Diez
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