Use of dict.pop in pm.sample leads to side effects

[jessegrabowski]

Description

I commonly create a sample_kwargs variable in notebooks and re-use it in multiple models. Such a dictionary ends up being modified in-place by pm.sample when entries are popped, for example here and here, leading to models beyond the first silently using defaults settings.

I guess the easiest fix would just be to deepcopy kwargs, so that there are no side effects on user inputs. Using pop here is a bit overkill (why not just ,get?) but deepcopy is a 1-line change.