Easier way to save result of a function?

[Alex Martelli]

Ant <antroy at gmail.com> wrote:

> > Thanks, that's awesome! Definitely not something I'd have ever been able
> > to work out myself - I think I need to learn more about nested functions
> > and introspection.
> 
> I've recently found nested functions incredibly useful in many places
> in my code, particularly as a way of producing functions that are
> pre-set with some initialization data. I've written a bit about it
> here: http://antroy.blogspot.com/ (the entry about Partial Functions)
> 
> > > def memoizeMethod(cls, n, m):
> > >   def decorated(self):
> > >     if n in self._memo: return self._memo[n]
> > >     result = self._memo[n] = m(self)
> > >     return result
> > >   decorated.__name__ = n
> > >   setattr(cls, n, decorated)
> 
> Couldn't this be more simply written as:
> 
>  def memoizeMethod(cls, n, m):
>    def decorated(self):
>      if not n in self._memo:
>           self._memo[n] = m(self)
>      return self._memo[n]
>    decorated.__name__ = n
>    setattr(cls, n, decorated)

Yes, at a tiny performance cost (probably hard to measure), though I
would spell the guard "if n not in self._memo:" :-).


> I've not seen the use of chained = statements before. Presumably it
> sets all variables to the value of the last one?

It sets all ``variables'' ("left-hand sides", LHS) to the right-hand
side (RHS) value; here, it lets you avoid an extra indexing in order to
obtain the value to return (a tiny cost, to be sure).


Alex