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

Replace

cache=[]
def match(v):

with

def match(v,cache=[])

Explanation: Your code declares cache as a variable of get_match, which the returned match(v) knows nothing about (due to the following assignment). You do however want cache to be part of match's namespace.

I know this way a "malevolent" user could redefine cache, but that's their own mistake. Should this be an issue though, the alternative is:

def match(v):
     try:
         if cache:
             return cache
     except NameError:
         cache = []
     ...

(See here)