summation interval. The return value is the
    expectation of the function, `func`, conditional on being in
    the given interval (k such that ``lb <= k <= ub``).
    Default is False.
maxcount : int, optional
    Maximal number of terms to evaluate (to avoid an endless loop for
    an infinite sum). Default is 1000.
tolerance : float, optional
    Absolute tolerance for the summation. Default is 1e-10.
chunksize : int, optional
    Iterate over the support of a distributions in chunks of this size.
    Default is 32.

Returns
-------
expect : float
    Expected value.

Notes
-----
For heavy-tailed distributions, the expected value may or
may not exist,
depending on the function, `func`. If it does exist, but the
sum converges
slowly, the accuracy of the result may be rather low. For instance, for
``zipf(4)``, accuracy for mean, variance in example is only 1e-5.
increasing `maxcount` and/or `chunksize` may improve the result,
but may also make zipf very slow.

The function is not vectorized.

c