All, Consider the poisson distribution in stats.distributions: it requires a mandatory argument, `mu`, as the mean/variance of the distribution. All is fine, but the `loc` parameter is still available, and that's my problem. When `loc` is not 0, the mean becomes `mu+loc`, `.cdf(range(loc))==0`, but the variance stays `mu`. That's a bit confusing. I thought I could use `loc` as a way to control truncation, but that doesn't seem to work either: emulating zero-truncation by using `loc=1` gives a distribution with a mean `mu+1` when is should be `mu/ (1-exp(-mu))` (the exact expression for zero-truncation). In short, I don't really see any advantage in having a location parameter for the Poisson distribution. AAMOF, for any discrete distribution. I suggest we would implement some mechanism to force loc to 0 while outputting a warning. Any comment ? P.