Re: accumulator generators

On May 30, 1:04 pm, "Diez B. Roggisch" <de...@xxxxxxxxxxxxx> wrote:
Cameron schrieb:



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>

Because python's static analysis infers s as being a variable local to
bar in the second case - so you can't modify it in the outer scope.

In the future, you may declare

def bar(i):
     nonlocal s
     ...

Diez

thanks for the response. Just to make sure I understand- Is the reason
it works in the first case because s[0] is undefined at that point (in
bar), and so python looks in the outer scope and finds it there?

Cameron

.

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