How can I do this (from Perl) in Python? (closures)

[Nick Craig-Wood]

excord80 at gmail.com <excord80 at gmail.com> wrote:
>  I just came across http://www.perl.com/pub/a/2002/05/29/closure.html
>  and wanted to try the "canonical example of closures" in Python. I
>  came up with the following, but it fails:
> 
>  def make_counter(start_num):
>      start = start_num
>      def counter():
>          start += 1
>      return counter
> 
>  from_ten = make_counter(10)
>  from_three = make_counter(3)
> 
>  print from_ten()       # 10
>  print from_ten()       # 11
>  print from_three()     # 3
>  print from_ten()       # 12
>  print from_three()     # 4
> 
>  The error message is: "UnboundLocalError: local variable 'start'
>  referenced before assignment". The same thing happens if I omit start
>  and just use start_num directly.
> 
>  How can I do it in Python?

With a class is the best way IMHO.

class make_counter(object):
    def __init__(self, start_num):
        self.x = start_num
    def __call__(self):
        x = self.x
        self.x += 1
        return x

-- 
Nick Craig-Wood <nick at craig-wood.com> -- http://www.craig-wood.com/nick