Python: decorator specific argument (unrelated to wrapped function)?

Question

I'm looking to build a caching decorator that given a function caches the result of the function to a location specified in the decoration. Something like this:

@cacheable('/path/to/cache/file')
def my_function(a, b, c):
    return 'something'

The argument to the decorator is completely separate from the argument to the function it's wrapping. I've looked at quite a few examples but I'm not quite getting how to do this - is it possible to have an argument for the decorator that's unrelated to and not passed to the wrapped function?

Answer 1

The idea is that your decorator is a function returning a decorator.

FIRST Write your decorator as if you knew your argument was a global variable. Let's say something like:

-

def decorator(f):
  def decorated(*args,**kwargs):
      cache = Cache(cachepath)
      if cache.iscached(*args,**kwargs):
          ...
      else:
          res = f(*args,**kwargs)
          cache.store((*args,**kwargs), res)
          return res
  return decorated

THEN Write a function that takes cachepath as an arg and return your decorator.

-

def cache(filepath)
    def decorator(f):
      def decorated(*args,**kwargs):
          cache = Cache(cachepath)
          if cache.iscached(*args,**kwargs):
              ...
          else:
              res = f(*args,**kwargs)
              cache.store((*args,**kwargs), res)
              return res
      return decorated
    return decorator