Class Cache

Decorator function that can be used to cache any function/method.

Example::

    @cache('key', 5000, cache.ram)
    def f():
        return time.ctime()

When the function f is called, web2py tries to retrieve
the value corresponding to `key` from the cache of the
object exists and if it did not expire, else it calles the function `f`
and stores the output in the cache corresponding to `key`. In the case
the output of the function is returned.

:param key: the key of the object to be store or retrieved
:param time_expire: expiration of the cache in microseconds
:param cache_model: "ram", "disk", or other
    (like "memcache" if defined). It defaults to "ram".

Notes
-----
`time_expire` is used to compare the curret time with the time when the
requested object was last saved in cache. It does not affect future
requests.
Setting `time_expire` to 0 or negative value forces the cache to
refresh.

If the function `f` is an action, we suggest using
`request.env.path_info` as key.

Parameters
----------
request:
    the global request object

Overrides: object.__init__