Re: accumulator generators

On May 31, 4:19 am, Arnaud Delobelle <arno...@xxxxxxxxxxxxxx> wrote:
Cameron <cameronla...@xxxxxxxxx> writes:
I was reading this <a href="thishttp://www.paulgraham.com/icad.html";>Paul
Graham article</a> and he builds an accumuator generator function in
the appendix. His looks like this:

<pre>
def foo(n):
  s = [n]
  def bar(i):
    s[0] += i
    return s[0]
  return bar
</pre>

Why does that work, but not this:

<pre>
def foo(n):
  s = n
  def bar(i):
    s += i
    return s
  return bar
</pre>

Others have explained why, but this looks like "pythonized LISP" to
me.  I would rather use a generator function:

def foo(n):
    while True:
        n += yield n

Although the problem is that you can't send it values the first time
round!

bar = foo('s')
bar.next()
's'
bar.send('p')
'sp'
bar.send('am')

'spam'

But:

bar = foo(3)
bar.send(2)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't send non-None value to a just-started generator

I find the "pythonized LISP" solution more understandable, even
without the initial next() requirement. YMMV

George
.

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