Allow user to bypass the cache when calling the @cached-decorated coroutine

[theomart]

What do these changes do?

It allows the user of the cached decorator to choose a keyword argument he can pass to the decorated function to easily bypass the cache.

Are there changes in behavior for the user?

If bypass_kwarg is not specified, nothing changes for the user. The user can choose a different keyword for each decorated function to conveniently avoid conflicts with actual arguments passed to the non-cache related logic.

import aiocache
import asyncio

@aiocache.cached(bypass_kwarg='refresh')
async def decorated_function(a):
    await asyncio.sleep(3)
    return a
    
loop = asyncio.get_event_loop()
print(loop.run_until_complete(decorated_function('test')))
print(loop.run_until_complete(decorated_function('test', refresh=False)))
print(loop.run_until_complete(decorated_function('test', refresh=True)))

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
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    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[Dreamsorcerer]

Seems like a decent idea, let me know if you want to come back and finish this off.

I'm thinking it might be cleaner if we just add a method or something to the decorated object, so you'd just do: my_func.refresh(*args) or similar.

We could also just clear the cache beforehand, which looks like it can already be done with something like my_func.cache.delete(key). With calculating the key being the difficult part, so a helper method to do that would still be good, so you just do my_func.clear(*args).

[Dreamsorcerer]

I've opened #625 for this idea. Let me know if you want to work on it.