fn : function (default: identity mapping)
Function for which sum is calculated. Takes only one argument.
args : tuple
argument (parameters) of the distribution
lb, ub : numbers, optional
lower and upper bound for integration, default is set to the support
of the distribution, lb and ub are inclusive (ul<=k<=ub)
conditional : bool, optional
Default is False.
If true then the expectation is corrected by the conditional
probability of the integration interval. The return value is the
expectation of the function, conditional on being in the given
interval (k such that ul<=k<=ub).