On Fri, Oct 9, 2009 at 04:45, Steve Borho <st...@borho.org> wrote:
>
>
> On Thu, Oct 8, 2009 at 2:36 PM, Adrian Buehlmann <adr...@cadifra.com> wrote:
>>
>> On 08.10.2009 20:57, Steve Borho wrote:
>> > FYI
>> >
>> > I realized today that we need to explicitly 'return False' from all of
>> > our idle_add() callback routines.
>> > If the return result evaluates as True, the callback will be called
>> > endlessly.
>> >
>>
>> Maybe I'm totally wrong here, but...
>>
>> A function that does not explicitly return a value
>> returns None, which counts as False.
>>
>> Correct?
>>
>> So we have a problem only with functions that
>> return a value.
>
> Good question. I assumed Python worked like a shell and just returned the
> result of the last operation.
>
>>>> def foo():
> ... a=True
> ...
>>>> foo()
>>>> bool(foo())
> False
>
>
> Yep, you're right. We only need to be worried about functions that return a
> value. Though it wouldn't be a bad idea to return False in these functions
> as a way to document the way idle_add() routines are used by GTK+.
For instance, we use 'lambda' and call a function returns result
evaluates as True in it:
def hoge():
# do something
return True
bool(lambda: hoge())
In lambda function, it will return the result of expression without
explicit 'return' statement.
Some time ago, I've replaced it to normal function, but it has
possibility to go endless calling.
--
Yuki KODAMA
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