efaults to this distribution;
the mixed in distribution is call by name, so may depend on this distribution.</p><div class="fullcomment"><div class="comment cmt"><p>generates from the mixed in optional valued distribution with probability <code>weight</code>,
otherwise, or if the optional returns None, defaults to this distribution;
the mixed in distribution is call by name, so may depend on this distribution.
</p></div><dl class="attributes block"><dt>Definition Classes</dt><dd><a href="ProbabilityDistribu