Another newbie question

[Scott Johnson]

I've read the tutorial and I don't get lambda.

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"Tim Peters" <tim_one at email.msn.com> wrote...

> [Interrupting Michael Hudson's fine advice to inject a nit]
> 
> [Roey Katz]
> > this brings up another concern. Given
> > the following definition:
> >
> >    class A:
> >
> >       def __getattr__( self, name ):
> >         return -1
> >       def __setattr__( self, name, val ):
> >          self.__dict__[ name ] = val
> >
> > I see that self.__dict__ must be a special variable
> > in that setting it somehow avoids a recursive call
> > to __setattr__()?
> 
> [Michael]
> > Yup. Look in Objects/classobject.c around about line 580
> > if you want the gory details.
> 
> While true, it doesn't apply to Roey's example:  he's not setting __dict__.
> He's binding a key *of* self.__dict__; self.__dict__ itself is merely
> referenced.  So Roey should really be wondering why the reference to
> self.__dict__ isn't invoking __getattr__ (&, of course, that's also due to
> special-case __dict__ magic, but in __getattr__'s implementation).
> 
> I don't mean to be overly picky; it's just that the excruciating details are
> vital when mucking with __getattr__/__setattr__, and *any* small
> misconception about them will eventually bite hard.
> 
> > ...
> > Bizarrely,
> >
> > filter(dest.append,src)
> >
> > is probably more memory efficient (the map form conses up a
> > list of return values, but as append always returns None -
> > which is false - filter `rejects' every element) - but if
> > you write code like this, you deserve to lose.
> 
> Yes, pointing him to the most bizarre endcases of Python behavior will
> surely aid him in "resetting his brain" <wink>.
> 
> Guido gave some excellent semi-exasperated advice (similar in spirit to
> parts of Michael's advice that I've snipped) many moons ago, when the whole
> newsgroup was temporarily filled with msgs of this character:  he invited
> people to just *try* writing a Python program without using any __xxx__
> hooks.  I expect some people were amazed at how much easier their lives got!
> If he were to get that exasperated again today, I bet he'd expand his
> invitation to include avoiding map, filter, reduce and lambda too.
> 
> you're-not-ready-to-use-them-in-python-before-you're-
>     happy-without-them-ly y'rs  - tim
> 
> 
>