python closure with assigning outer variable inside inner function

Question

I\'ve got this piece of code:

#!/usr/bin/env python

def get_match():
  cache=[]
  def match(v):
    if cache:
      return cache
    cache=[v]
    return ca         


        

Answer 1

Since Python sees cache=[v] - assignment to cache, it treats it as local variable. So the error is pretty reasonable - no local variable cache was defined prior to its usage in if statement.

You probably want to write it as:

def get_match():
  cache=[]
  def match(v):
    if cache:
      return cache
    cache.append(v)
    return cache
  return match
m = get_match()
m(1)

Highly recommended readings: Execution Model - Naming and binding and PEP 227 - Statically Nested Scopes