Session per-variable expiration

[Alan Etkin]

It seems that some PHP library provides a way to specify when a session (or wathever PHP similar object) variable should be deleted. I did not find a web2py method to do that. Should we add this to the default session interface?

It would be something like:

def __init__(self):
    ...
    # controls expiration datetime
    self._vars_timeouts = dict()

def _clean_vars(self):
    "method to call after initialization"
    for var in self.keys():
        if <var expired>:
            <delete var>

def var_expires(var, datetime or timedelta):
    "update ._vars_timeouts for a given variable"
    ...