What's up with rebinding assignment?
jepler at unpythonic.net
Fri Mar 21 15:24:56 CET 2003
On Fri, Mar 21, 2003 at 01:53:25PM +0000, Des Small wrote:
> I wouldn't use it here though, I'd use it for things like:
> def accumulator(val=0):
> def inner_acc(amount):
> lexical val
> val = val + amount # I don't like +=, so there.
> return val
> return inner_acc(val)
> Since I don't expect the Python Priesthood (Bot-hood?) to be pleased
> about this, I would want to market it as a less harmful version of
> 'global'. It does do much the same thing, after all, and has much
> the same conventions.
You could also use it for a getter/setter factory:
val = initial_value
val = new_value
return (get, set)
However, in Python it's more natural to write these things as classes.
def __init__(self, val=0):
self.val = val
def __call__(self, amount):
self.val = self.val + amount
# Using lambda to prove I don't hate lisp
accumulator = lambda val=0: Accumulator(val).__call__
I suspect that the closure-based version would be slightly more
efficient if it were writable, since the natural way to use Accumulator
would create a bound method at each call, and the references to 'val' in
__call__ are all namespace operations. I *think* that the cell
operations are simple C array indexing when executed, and if that's
true, I don't see why the cell-setting instruction wouldn't be.
More information about the Python-list