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